MOP2011-P0056
Oral (Invited)
Titan's Plasma Environment and Interaction
Bertucci, C. [1]
[1] Institute for Astronomy and Space Physics, Astrophysical Plasmas
With a negligible internal field and an extended, dense atmosphere, Titan's
interaction with its plasma environment is atmospheric. This interaction, however, has
been shown to be extremely non-stationary as the moon's plasma environment is
subject to significant degree of variability, most of it, on timescales of the order of the
upstream plasma transit times. Solar wind dynamic pressure, and factors altering the
static local stress balance at the Kronian magnetodisk are responsible for this
variability. The presence of an ionosphere and exospheric massloading reduce the
upstream plasma transit time near the moon and the magnetic environment history is
recorded in its induced magnetosphere. However, Titan's ionosphere is an intricate
electromagnetic system where ion-neutral collisions
play a key role in the balance
between magnetic transport and diffusion and where induced currents could
significantly alter the expected topology of the external magnetic field. In this talk we
review and discuss some of the most relevant results on which these interpretations
are based.
MOP2011-P0091
Oral (Invited)
Cassini VIMS Observations of Saturn's Infrared Aurora
Badman, S. [1] and M. Cassini [2]
[1] JAXA, ISAS
[2] Cassini, Cassini
The Cassini Visual and Infrared Mapping Spectrometer is obtaining infrared images
and spectra of Saturn at unprecedented spatial and temporal resolution. In this talk
we highlight observations to date of Saturn's H3+ auroral emissions.
These include (a)
the detection of bright polar 'infilling' emissions inside the main oval region, which are
unlike any seen in the UV data; (b) characterisation of the location of the main oval
emissions, which are found to lie at the same location as the UV main oval thus
indicating a common driving field-aligned current; (c) latitudinal and hemispheric
differences in the IR emitted intensity pre-equinox, and resulting implications for the
significance of Joule heating and 'polar rain' in generating IR emission.
MOP2011-P0003
Oral (Invited)
The role of the atmosphere in ionosphere-magnetosphere coupling
Achilleos, N. [1]
[1] UCL, Physics and Astronomy
A rich body of work has been produced regarding global circulation models of giant
planet thermospheres, and their role in magnetosphere-ionosphere coupling. In this
talk, we summarise some of the important recent developments in modelling the
thermospheres of Jupiter and Saturn. In particular, we examine how aspects of
thermospheric flow can 'feed back on' and modify the magnetospheric rotation rate.
We shall consider the effects of a change in magnetospheric configuration on
thermospheric flow at Jupiter, and its consequences for the global energy budget of
the coupled system. Finally, we shall present results of a simple, time-dependent
simulation using the UCL Saturn model, which show that very disturbed auroral
patterns may arise when one considers the finite response time of the thermosphere
to rapid changes in the magnetospheric plasma rotation.
MOP2011-P0005
Oral (Invited)
The Saturnian Ring Current
Sergis, N. [1]
[1] Academy of Athens, Office of Space Research
The Saturnian ring current, initially inferred from magnetic field and particle
measurements during the Voyager 1 and 2 flybys, has been studied in more detail
since
July
2004,
when
Cassini
started
orbiting
the
planet,
monitoring
its
magnetospheric environment via in-situ and remote measurements. It is located
between 8 and 15 RS, primarily composed of O+ ions, characterized by increased
suprathermal (>3 keV) particle pressure with high (>1) plasma β values and intense
dynamic behavior, as revealed by the continuous analysis of combined particle data
from the Cassini Magnetospheric Imaging Instrument (MIMI) and the Cassini Plasma
Spectrometer instrument (CAPS), and magnetic field measurements from the Cassini
magnetometer (MAG). Among the most important findings so far is that the azimuthal
ring current is primarily inertial inside about 8 R S, but increasingly pressure gradient
driven in its maximum region (8 to 12 RS, 100 to 150 pA/m2) and certainly farther out,
dropping, however, with radial distance faster than the often the previously assumed
1/r rate and causing a magnetic perturbation of 10 to 15 nT. The 7 year worth of
Cassini data offers today a much better (yet not complete) spatial coverage,
permitting a more comprehensive study of still open issues such as the local time
asymmetry of the ring current properties, the accurate estimation of the relative
contribution of different components in the radial force balance and the plasma
pressure distribution in the equatorial magnetosphere. New (2011) results are
presented, including analysis of individual orbits of special interest and organization of
the data in the SLS4 longitude system. Finally, energetic neutral atom (ENA) images
from the Ion and Neutral Camera (INCA) of Cassini, provide a unique overview of a
large part of the Saturnian magnetosphere, depicting, for the first time, the rotation
and partial nature of the ring current.
MOP2011-P0008
Oral (Invited)
Tutorial: Aurora - Micro Processes
Hess, S. [1]
[1] LATMOS, UVSQ, IPSL/CNRS
Auroral emissions are the consequence of current systems generated in the
magnetosphere that close in the planet ionosphere. More precisely, the current along
the magnetic field lines creates parallel electric fields that accelerate electrons,
which in turn generate emissions. The current systems in the magnetospheres and the
aurorale features will be presented in other tutorials. In the present one, we focus on
the mechanisms responsible for the electron acceleration, on their relation with the
current characteristics and their consequences in terms of auroral emissions.
MOP2011-P0010
Oral (Invited)
Energetic charged particle absorption signatures
magnetosphere: observations and applications
in
Saturn's
Roussos, E. [1], N. Krupp [1], M. Andriopoulou [1], P. Kollmann [1], C.P. Paranicas [2],
M.F. Thomsen [3], D.G. Mitchell [2] and S.M. Krimigis [2,4]
[1] Max Planck Institute for Solar System Research, [2] John's Hopkins University Applied Physics Laboratory, [3] Los Alamos National Laboratory, [4] Academy of Athens, The local interaction region of a planetary moon with its surrounding magnetospheric
plasma environment is typically contained within several moon radii upstream and/or
downstream of the moon's position. Signatures of this interaction in energetic particles,
however, can be observed at very large distances from their point of origin. At such
large distances from the moon, the evolution of these signatures reflects properties of
global magnetospheric environment and its dynamics, rather than that of the
disturbances within the moon interaction region. It is therefore apparent that the study
of these distant signatures can be used to extract fundamental information about the
configuration and the dynamics of the magnetosphere. For instance, the refilling rate
of these absorption features can be associated with particle diffusion. In addition, as
these structures drift, mapping their location can provide us direct information on the
particle drift shell structure and the factors that influence their shape. In Saturn's
magnetosphere, these distant features appear in the form of localized dropouts in
energetic electron fluxes (microsignatures). Using data from Cassini's MIMI/LEMMS and
CAPS/ELS detectors we have catalogued more than 250 microsignature events to
date, at more than 20 energy channels per event on average , covering an energy
range from several hundred eV up to several MeV. In this talk we will demonstrate the
power of this (continuously growing) dataset by presenting a large number of
applications and results for Saturn's magnetospheric configuration and dynamics. We
will aslo highlight the importance of similar observations for future missions, such as
Juno or EJSM.
MOP2011-P0011
Oral (Invited)
Magnetosphere: Structure and Dynamics
Kivelson, M.G.[1]
[1] UCLA, Dept Earth and Space Sciences
[2] University of Michigan, Dept Atmospheric, Oceanic, and Space Sciences
Whether it is an end game in chess or today's Sudoku, most of us like to solve puzzles.
As we try to understand what is going on in the magnetospheres of the gas giants,
Jupiter and Saturn, many of us manage to work and play at the same time. What
questions do we play with? There are many. In both systems, the principal mass
sources are well established, but the processes that change the energy density of the
plasma as it moves outward from its source are not fully understood. In both systems,
impulsive injections are frequent but it is not yet clear just what controls them.
Still
disputed at Jupiter is the importance of the solar wind interaction and the degree to
which the magnetosphere is open to the interplanetary magnetic field.
Periodicities
take the pride of place at Saturn and multiple theories contend in providing
explanations.
Of particular interest to the speaker is the possibility that Saturn's
ionosphere may be the primary source of periodic behavior observed in many
properties of the magnetosphere. Even at Jupiter, tantalizing hints of System IV
periodicities suggest that processes evident in Saturn's magnetosphere with an
axisymmetric central field may be present at Jupiter as well, largely hidden by the
dominant variations arising from a tilted internal field.
Increasingly it is clear that at
Saturn (and possibly at small radial distances at Jupiter), dust affects the dynamics of
the system in ways that have not yet been fully incorporated into models. This talk
will largely ignore the aspects of the systems on which there is general agreement and
address primarily aspects of structure and dynamics that are not yet fully understood.
MOP2011-P0017
Oral (Invited)
Aurora : Global Features
GERARD, J.M.[1]
[1] Universite de Liege, LPAP
Auroral emissions are excited by collisions between (primary and secondary) auroral
electrons and atmospheric species. Observations of Jupiter's aurora with the Hubble
Space Telescope over two decades have provided information on the morphology
and dynamics of the aurora and energy of the precipitating particles. HST UV images
have shown that the size and brightness of the Jovian main oval shows a weak
dependence on solar wind conditions. It appears relatively shielded from solar wind
influences, except polar emissions inside the auroral oval where transient bright
emission has been observed. By contrast, Saturn's aurora is quite responsive to solar
wind perturbations, as was observed during campaigns of concurrent observations
between HST and Cassini. Several features of Jupiter's and Saturn's aurora reflect
processes at play in the magnetospheres: - the magnetospheres of the outer planets
are dominated by the planetary rotation that can provide much of the energy for the
processes acting within these magnetospheres. - the circulation of plasma may be
driven by mass loading of the giant magnetospheres by moons and rings rather than
by reconnection with the IMF.
- the magnitude and orientation of the interplanetary
magnetic field plays a key role in controlling the Earth's auroral dynamics whereas the
solar wind dynamic pressure appears as a key factor in triggering
auroral
intensification on Saturn. Observations of transient and variable spots in the vicinity of
both planetary main emission have been interpreted as signatures of magnetic field
line reconnection. Recently, periodic brightening of the Jovian polar region (polar
flares) has been interpreted as resulting from pulsed reconnections occurring at the
dayside magnetopause. Observations of the altitude of the aurora above the limb
and combined HST, FUSE and UVIS spectroscopy are currently the only tools available
to remotely probe the energy of auroral particles. The combination of imaging and
spectral techniques indicates that the characteristic energy of the auroral electrons is
comparable on Earth and Saturn, but higher energies are associated with the Jovian
aurora.
MOP2011-P0030
Oral (Invited)
Neutral Atmosphere - Ionosphere - Magnetosphere Coupling
Galand, M. [1], I. Mueller-Wodarg [1], L. Moore [2], M. Mendillo [2], S. Miller [3] and L.
Ray [1]
[1] Dpt of Physics, Imperial College London
[2] Center for Space Physics, Boston University
[3] Dept of Physics and Astronomy, University College London
The presented tutorial will focus on the neutral atmosphere - ionosphere magnetosphere coupling in the context of the energy crisis at the giant planets. The
energy crisis refers to the significantly larger values of observed exospheric
temperatures at low- and mid-latitudes compared with those computed and derived
from
solar
heating
alone.
We
will
discuss
the
importance
of
magnetosphere-ionosphere coupling as a heating source of the upper atmosphere
at high latitude through Joule heating and the subsequent redistribution of energy
towards lower latitudes. Auroral ionospheric, electrical conductances at Saturn will be
assessed and their sensitivity with the mean energy and energy flux of the incoming
auroral electrons, evaluated. Their values are significantly larger than those derived in
the auroral regions of Earth and Jupiter. We will explain the main reasons for this
difference and discuss its implications on magnetosphere-ionosphere processes. We
will next highlight how observations from Earth and from the Cassini spacecraft as well
as those expected from the Juno mission could further constrain the missing energy
source at Saturn and Jupiter. Finally, outstanding problems in the field will be identified
for the four giant planets.
MOP2011-P0071
Oral (Invited)
The chiming of Saturn's magnetosphere at planetary periods.
Provan, G. [1]
[1] University of Leicester, Physics and Astronomy
Saturn's magnetosphere chimes with oscillations at periods close to the planetary
rotation period.
The oscillatory period changes slowly over time [Galopeau and
Lecacheux, 2000; Gurnett et al., 2005, Kurth et al., 2007, 2008], with slightly different
periods being observed in the Northern and southern hemispheres [Gurnett et al.,
2009a, Lamy, 2010].
2011].
Both periods are observed in the equatorial plane [Provan et al.,
This talk aims to explore the periodicity, phase and polarization of magnetic
field oscillations on closed and open field lines, and show how these oscillations are
related to the variations in the UV auroral power as observed by the Hubble
spacecraft [Nichols et al., 2010a], the location of the UV auroral oval [Nichols et al.,
2008,2010b, Provan et al., 2009], the position of the magnetopause and bow shock
[Clarke et al., 2006, 2010a,b] and the flapping of Saturn's plasma sheet [Arridge et al.,
2011]
MOP2011-P0078
Oral (Invited)
The Response to the Solar Wind of the Jovian and Saturnian Auroras
Clarke, J.T.[1]
[1] Boston University, Center for Space Physics
This talk will give an overview of observations of auroral activity on Jupiter and Saturn
and how they have been observed to correlate with solar wind conditions at each
planet. In addition to the large HST program and observing campaigns in 2007 and
2008, there have been more recent observing campaigns of Saturn involving HST,
Cassini, and ground-based telescopes. The large set of concentrated observations
in recent years has led to other discoveries, in addition to the identification of
correlations with the solar wind. The new data sets also make it possible to derive
better statistics on the various auroral emissions and processes.
New observations of
the magnetic footprints of the Galilean satellites at Jupiter, and the Cassini detection
of auroral emission from the magnetic footprint of Enceladus on Saturn, will also be
presented.
MOP2011-P0105
Oral (Invited)
Modeling of Large-scale systems: The Magnetospheres of Jupiter and
Saturn
Hansen, K. [1]
[1] University of Michigan, AOSS
Building a first principles based numerical model of any system is a complex task
requiring broad understanding of both the physics of the system as well as the
strengths and limitations of different numerical techniques.
In many ways,
developing, testing, maintaining and using an advanced numerical model is similar to
the development and deployment of spacecraft instruments and the interpretation
and use of their data. In this talk we will highlight some of the challenges that are
encountered in modeling large-scale systems such as outer planet magnetospheres.
Items we will address include:
challenges of underlying physics, numerical trade-offs,
development costs and required simulation resources.
Finally, it is clear that
large-scale simulations of both Saturn and Jupiter have helped further our
understanding of their magnetospheres. To emphasize this point, we will highlight a
few interesting results from the various different global magnetosphere models.
MOP2011-P0112
Oral (Invited)
Observations of Plasma Sheet Structure and Dynamics
Arridge, C. [1,2]
[1] Mullard Space Science Laboratory, University College London
[2] The Centre for Planetary Sciences, UCL/Birkbeck
The global near-equatorial plasma sheets at Jupiter and Saturn are filled with plasma
from internal mass sources in the magnetosphere. These plasma sheets are important
in regulating the transport and loss of plasma from the magnetosphere, and in
heating plasma and accelerating energetic particles. The location of the plasma
sheet is complex and highly time dependent and is forced both by the solar wind and
internal magnetospheric processes. This internal forcing is provided by centrifugal
stresses, dynamics, and periodicities generated by the rotation of the planet at Jupiter
and by global magnetospheric periodicities at Saturn. Centrifugal forces are also
important in determining the structure of these sheets, producing ion composition
gradients normal to the sheet surface. Dynamical processes have been observed at
Jupiter and Saturn which include: transient waves, tearing, outflows and plasmoids
from magnetic reconnection, observations of transient cold plasma blobs, and
time-variability in the thickness of the sheet. In this talk we will review the basic physical
processes involved in forcing these sheets and generating dynamics, and discuss the
latest observations of these plasma sheets.
MOP2011-P0113
Oral (Invited)
Dust Observations at Rhea and Enceladus using Plasma Instrumentation
Jones, G.H.[1,2]
[1] Mullard Space Science Laboratory, University College London
[2] Centre for Planetary Sciences at UCL/Birkbeck, Gower Street
The dust environments of Saturn's icy moons can be probed by several of Cassini's
instruments. As well as the dedicated dust instrument, CDA, and the radio and plasma
wave instrument RPWS, both of which have, as expected, proven highly successful in
making observations of dust in the Saturnian system, other Cassini instruments have
also proven their great worth in making measurements of dust using complementary
techniques. Following the successful detection of heavy negative ions in Titan's upper
atmosphere by the Cassini Plasma Spectrometer's electron spectrometer, all of the
CAPS sensors were found to be effective detectors of charged nanograins in the
plume of Enceladus. When oriented in the ram direction, both positive and negative
charged grains entering the instrument at the relative encounter speeds of ~6-18 km/s
can be detected by the three CAPS sensors. A review is given of these direct charged
nanodust observations at Enceladus, and their implications for our understanding of
the plume. Dust can absorb energetic charged particles, and the resulting absorption
signatures can be detected by CAPS and very effectively by the magnetospheric
imaging instrument, MIMI. An overview of absorption signatures caused by the
Enceladus plume will be presented, changes in them indicate variations in the activity
of the plume. At Rhea, a broad energetic electron depletion was observed by MIMI,
which was suggested to be caused by absorption of the electrons by a debris disk
surrounding the moon. Our interpretation of this and other perplexing signatures
observed near Rhea will be presented, in the context of a lack of supporting imaging
evidence of a dust population surrounding Saturn's second-largest moon.
MOP2011-P0116
Oral (Invited)
Global Magnetospheric Dynamics of Jupiter and Saturn Revealed by
ENA Imaging
brandt, p.c.[1], d.g. mitchell [1], b.h. mauk [1], c.p. paranicas [1] and N. Krupp [2]
[1] Space Department, JHU/APL
[2] -, Max-Planck Institute for Solar System Research
In this presentation we review how ENA images obtained by the Ion Neutral Camera
(INCA) on board Cassini has helped us understand the global dynamics and transport
of energetic particles in the Saturnian magnetosphere [Brandt et al., 2008] and how
they relate to other phenomena such as periodic radio emissions, auroral emissions
[Mitchell et al., 2009], and periodic field perturbations [Khurana et al., 2009; Provan et
al., 2009; Brandt et al., 2010]. Given the success of ENA imaging at Saturn, we discuss
how this success can be repeated by the potential Jupiter Ganymede Orbiter (JGO).
The Jovian magnetosphere has already been successfully imaged in ENAs by INCA
during the Cassini fly-by (closest approach ~120 RJ ) and it is clear that ENA imaging
would provide game-changing insights in to the existence of quasi-periodic injections
[Woch et al., 1998; Selesnick et al., 2001], their relation to narrow-band and hecto
metric radio emissions [Louarn et al., 2007], the interaction between global energetic
ion distributions with the neutral gas torus region of Europa, and how that can be used
to constrain the dynamics, source and morphology of the Io and Europa torus
distributions. However, the Jovian magnetosphere is also a very harsh radiation
environment that presents limits to what is technically feasible. To address these issues,
we use past measurements and a data-derived model to simulate ENA images
through a realistic camera response function along candidate orbits.
MOP2011-P0123
Oral (Invited)
Dust and Low Temperature Plasma of Saturn
Morooka, M.W.[1], J. Wahlund [1], M. Shafiq [1], W.M. Farrell [2], D.A. Gurnett [3], W.
Kurth [3], A.M. Persoon [3], M. Andr? [1], A. Eriksson [1], M.K. Holmberg [1] and S.
Sakai [4]
[1] Uppsala, Swedish Institute of Space Physics
[2] Planetary Magnetospheres Laboratory, NASA/Goddard SFC
[3] Department of Physics and Astronomy, University of Iowa
[4] Department of Cosmoscience, Hokkaido University
The icy moons and rings of Saturn are a source of the dust, neutral gas, and plasma in
Saturn's magnetosphere. Many observations indicate that origin of the rotational
modulation of Saturn's magnetosphere is located in the inner magnetosphere near
Enceladus orbit. It is a major discovery by Cassini that water ice expelled from
Enceladus play major role in Saturn's magnetosphere. A striking feature is that small E
ring grains are negatively charged and couples to the ambient plasma electrically.
We will present the dynamics of the charged dust and the plasma in the plasmadisc.
A large ion and electron density difference (Ne/Ni < 0.01-0.5) that is associated with
the micrometer sized dust grains is observed near Enceladus plume and the E ring
region. This is due to the electron attachment to the dust grains and thus the dust is
negatively charged. The RPWS/LP is designed to measure the cold (few eV) electron
and ion and indicated an existence of dense cold plasma. In addition, the bulk ion
speed was significantly slower than the co-rotation speed and close to the
gravitational speed. An interpretation to this slow ion is that the cold ions are trapped
in the electric potential of the charged dust and moves in a same speed as the dust,
i.e. the dust-plasma interaction is collective. The dust and plasma properties
estimated from the observations clearly show the strong dusty plasma characteristics.
We will discuss the dust-plasma interaction in the E ring and its relation to the dynamics
of Saturn's outer magnetosphere.
MOP2011-P0133
Oral (Invited)
Dust measurements with CDA on Cassini
Kempf, S. [1], R. Srama [2], G. Moragas-Klostermeyer [2], J. Schmidt [3], F. Spahn [3]
and F. Postberg [4]
[1] LASP, Colorado University at Boulder
[2] IRS, Stuttgart University
[3] Physics, Postdam University
[4] Institute for Geoscience, Heidelberg University
Saturn's diffuse E ring is the largest ring of the solar system and extends from about
3.1Rs (Saturn radius Rs = 60330 km}) to at least 20 Rs encompassing the icy moons
Mimas, Enceladus, Tethys, Dione, and Rhea. After Cassini's insertion into its Saturnian
orbit in July 2004, the spacecraft performed a number of equatorial as well as steep
traversals through the E ring inside the orbit of the icy moon Dione.
Dust Analyser (CDA) determines
The Cosmic
the mass, speed, and charge of dust grains striking
the target of the instrument. Furthermore, compositional information is collected by
the Chemical Analyser (CA) subsystem.
Here, we report about dust impact data
obtained by the Cosmic Dust Analyser (CDA) during almost equatorial passages
through the E ring in early 2010. CDA determines the mass, speed, and charge of dust
grains striking the target of the instrument. Furthermore, compositional information is
collected by the Chemical Analyser (CA) subsystem. We acquired for the first time
radial density profiles of the entire inner E ring, which show no density enhancements
at the orbital distances of the embedded ring moons Tethys, Dione, and Rhea. The
densest point of the ring could be determined with high accuracy. Our analysis
suggests that the vast majority of the ring particles originates from the Enceladus dust
plume. We also report about measurements during the close Cassini flybys at the ring
moons Enceladus and Rhea. These data provides new insights into the particle
production by embedded ring moons.
MOP2011-P0137
Oral (Invited)
Satellites and interactions
Delamere, P. [1]
[1] University of Colorado, Laboratory for Atmospheric and Space Physics
The interaction of a satellite and its plasma environment results in a cascade of
physical processes that couple the satellite to the distant planetary atmosphere.
A
key aspect of this topic are the complex electrodynamic processes that result from
the interaction of inflowing plasma with neutral gas distributed near the satellite.
neutral gas can be in the form of,
for example,
The
a gravitationally bound
atmosphere (e.g. Io) or an escaping plume (e.g. Enceladus).
A directly-observable
consequence of the plasma/neutral interaction are auroral emissions both at the
satellite and/or at the magnetic footprint of the satellite in the planetary atmosphere.
In this review, we will focus on aspects of the local electrodynamic interaction (i.e.
within several satellite radii)
that ultimately generate the large-scale current systems
that couple the satellite to the planetary atmosphere as well as implications for the
circumplanetary distribution of neutral gas.
MOP2011-P0070
Oral (Invited)
Saturn's rotation
Lamy, L. [1]
[1] Observatory of Paris, LESIA
The diurnal modulation of magnetospheric phenomena at Jupiter, Uranus or Neptune
mainly results from the tilt of the dipole axis relative to the rotation axis. In the case of
Saturn however, the magnetic and rotation axes are nearly aligned, so that the
existence (and the persistence) of a strong periodic signal at ~10.8h, observed
ubiquitously in the magnetosphere since the Voyager epoch, is challenging our
understanding of the kronian system. This picture would remain relatively simple if
Ulysses and especially Cassini had not revealed an even more intriguing situation.
Indeed, each hemisphere seems in fact to be mainly modulated at its own period
(near ~10.8h for the southern hemisphere, and ~10.6h for the northern one over
2004-2009), while both periods vary with time in an anti-correlated manner over years
until they come close to each other near equinox. This unexpected situation, up to
now unique in the solar system, has driven considerable debate on the nature, the
origin and the co-existence of these periodicities, and their relationship with the deep
interior of the planet. In this tutorial, I will tentatively review the various observational
evidences of Saturn's periodicities in both remote and in situ measurements as well as
theoretical efforts proposed to account for these phenomena.
MOP2011-P0006
Oral (Invited)
Auroral X-ray Emission at the Outer Planets
Ozak, N. [1], T.E. Cravens [1], Y. Hui [2], D.R. Schultz [2] and V. Kharchenko [3]
[1] Dept. of Physics and Astronomy, University of Kansas
[2] Physics Division, Oak Ridge National Lab
[3] Atomic and Molecular Physics Division, Harvard Smithsonian Center for Astrophysics
Jupiter's aurora is known to be a powerful source of radio, infrared, visible, ultraviolet,
and x-ray emission. In particular, Jovian auroral x-ray emissions with a total power of
about 1 GW have been observed by the Einstein Observatory, the Roentgen satellite,
Chandra X-ray Observatory and XMM-Newton.
The ultraviolet auroral oval in Jupiter
has been demonstrated to be produced by energetic electron precipitation
associated with co-rotation lag in the middle magnetosphere. Some hard x-ray
emission from the main oval has also been observed by XMM-Newton, probably due
to electron bremsstrahlung. However, most x-ray power is in soft x-rays emitted at the
polar caps. Two possible mechanisms have been suggested as the source of these
emissions: (1) cusp entry and precipitation of solar wind heavy ions and (2)
acceleration and subsequent precipitation of magnetospheric ions. Recent
theoretical studies of energetic oxygen and sulfur ion precipitation into the Jovian
atmosphere as well as observations of line spectra containing lines from high
charge-state oxygen and probably sulfur support the second mechanism as the x-ray
emission source. Observations of Saturn also revealed the presence of an ultraviolet
aurora, but no x-ray emissions have been observed yet. This paper reviews the
theoretical and observational aspects of the x-ray aurora in Jupiter and Saturn and
explores its implications for the magnetosphere-ionosphere coupling.
MOP2011-P0023
Oral (Contributed)
Saturn's North and South aurora observed by Cassini camera in visible
wavelengths
Dyudina, U. [1], A.P. Ingersoll [1], D. Wellington [1], S.P. Ewald [1] and C.C. Porco [2]
[1] Planetary Science, Caltech
[2] CICLOPS, Space Science Institute
We present 2009-2010 movies from the Cassini camera showing Saturn's aurora in both
the northern and southern hemispheres. The observations reveal reddish color of the
aurora observed in filters spanning different wavelengths from 250 nm to 1000 nm. The
prominent H-alpha line and the overall spectral shape agrees with predicted spectra
for Saturnian auroras (Aguilar, 2008). Two 400+ frame movies, one in the northern
hemisphere from October 5-9, 2009, and the other in the southern hemisphere, from
June 26, 2010, ?show the aurora varying dramatically with longitude and rotating
together with Saturn. The main longitudinal structure of the aurora can persist for more
than 3 days, as seen on the repeated views of the same longitudes several Saturn
rotations later. Besides the steady main structure, aurora may brighten suddenly on
the timescales on the order of 10 minutes. Near the limb the height of the auroral
curtains above its base can be measured; this height can reach more than 1200 km.
The main auroral oval in the northern hemisphere appears near 75° latitude. The main
auroral oval in the southern hemisphere appears near -72° latitude, with smaller
instances of auroral activity near -75° and -77°. The stability of the longitudinal auroral
structure allowed us to estimate its period of rotation to be 10.65 &plusmn 0.05 h,
which is consistent to the SKR period detected by Cassini in 2009. These periods are
also close to the rotation period of the lightning storms on Saturn. We will discuss those
periodicities and their relation to Saturn's rotation.
Reference: Aguilar, A., J. M. Ajello,
R. S. Mangina, G. K. James, H. Abgrall, and E. Roueff, The electron-excited middle UV
to near IR spectrum of H2 : Cross-sections and transition probabilities, Astrophys. J.
Supp. Ser., 177 (2008).
MOP2011-P0043
Oral (Contributed)
Open-Closed Field Line Boundary Characterization of
Magnetosphere Using Cassini MIMI-LEMMS Data And
Observations From HST And Cassini-UVIS
Saturn's
Auroral
Krupp, N. [1], A. Radioti [2], E. Roussos [1], D. Grodent [2], D.A. Gurnett [3], D.G.
Mitchell [4] and M.K. Dougherty [5]
[1] Planetary Department, Max-Planck-Institut f?r Sonnensystemforschung
[2] Laboratoire de Physique Atmospheric et Planetaire, Universite de Liege
[3] Department of Physics and Astronomy, University of Iowa
[4] Applied Physics Laboratory, The Johns Hopkin
The high-latitude open-closed field line boundary at Saturn is thought to be related to
the main auroral ring of emission of the planet. In this presentation we use
bi-directional energetic electron distributions from the MIMI-LEMMS instrument
onboard Cassini and auroral observations from the Hubble Space Telescope (HST)
and the UVIS instrument onboard Cassini to characterize this boundary. The main ring
of emission at Saturn has been shown to vary in location, intensity and latitudinal
extent as well as in its homogeneity.
This study extends the work on the
plasmapause/open-closed field line boundary published by Gurnett et al., GRL, 2010,
by covering a larger data set at different local times and comparing the electron
distributions with auroral observations.
Based on energetic electron data we
characterize the open-closed field line boundary in terms of temporal, local time
variations and other parameters and we correlate the Cassini in-situ measurements to
the observations of the main auroral ring at Saturn.
MOP2011-P0108
Oral (Contributed)
Time Variability of the Saturn's Ring Atmosphere and Ionosphere
Tseng, W. [1], M.K. Erlod [1], R.E. Johnson [1] and W. Ip [2]
[1] University of Virginia, Materials Science and Engineering
[2] National Central University, Astronomy
The detection of O2+ and O+ ions over Saturn's main rings by the Cassini INMS and
CAPS instruments at SOI confirmed the existence of the ring atmosphere and
ionosphere. The source mechanism was suggested to be
primarily photolytic
decomposition of water ice tproducing neutral O2 and H2 (Johnson et al., 2006).
Therefore, we have predicted that there would be seasonal variation for the ring
atmosphere and ionosphere (Tseng et al., 2010). However, the situation is also
complicated by water products from the Enceladus' plumes, which, although
variable,
do not appear to have a seasonal variability (Smith et al., 2010). That is, the
deposition of OH and O from the Enceladus' plumes onto the A-ring can also produce
O2 through grain-surface chemistry contributing to the ring atmosphere (Tseng and Ip,
2011). The non-detection (or upper limit) of H2+ ions over the B-ring by the Cassini
CAPS has helped constrain the source rates . Now the importance of the seasonal
variation is being tested by our examination of the CAPS plasma data between 2.5
and 3.5 RS from 2004 to 2010 (Elrod et al. 2011). We have shown that there are
significant variations over that time period in the plasma density and composition.
Since the ring atmosphere is also affected by the ring particle temperatures, which
were ignored in our earlier model, and, possibly, by solar high energy particle
radiation, we developed a one-box ion chemistry model to explain the complex and
highly variable plasma environment that was observed by the CAPS instrument on
Cassini.
MOP2011-P0004
Oral (Contributed)
Post-Equinox Saturn Magnetic Rotation
Southwood, D. [1]
[1] Imperial College, Physics Department
During late 2009 and 2010 the Cassini spacecraft remained in a low latitude orbit
providing a good platform for analysis in the inner magnetosphere of the periodic
magnetic signals associated with planetary rotation.
The epoch immediately
follows the Saturn equinox. During the time in question it has already been reported
that the periods of the northern and southern SKR radio signals appear to come
together whilst the mean frequency appears fairly stationary. Here we report on
analysis of what happens to the corresponding periodic magnetic signals seen by the
spacecraft. It is shown that the period signals in the magnetic field have a fixed
primary period of close to 642.3 minutes during the period in question matching well
the period corresponding to the mean radio frequency. It is also shown that rapid
changes in phase of order half a cycle take place between periapsis passes. It is
argued that in contrast with earlier analyses before equinox where the Southern
period dominated it would seem now that Northern and Southern amplitudes are now
about equal.
discussed.
The nature of the underlying magnetospheric signal structure will be
MOP2011-P0007
Oral (Contributed)
Plasma interactions of Saturn's icy satellites: Analytical modelling of
Cassini MAG data from Enceladus, Dione and Rhea
Simon, S. [1], J. Saur [1], F. Neubauer [1], H. Kriegel [2] and M. Dougherty [3]
[1] University of Cologne, Institute of Geophysics and Meteorology
[2] University of Braunschweig, Institute for Theoretical Physics
[3] Imperial College London, Space and Atmospheric Physics Group
We present an analytical model for the magnetic field perturbations that arise from
the interaction of Saturn's icy satellites Enceladus, Dione and Rhea with the corotating
plasma in the giant planet's inner magnetosphere. It is demonstrated that electron
absorption by submicron dust grains within the plume plays a crucial role in
understanding the field signatures measured near Enceladus. This process gives rise to
a reversal in the sign of the Hall conductivity (Anti-Hall effect), thereby yielding a twist
of the magnetic field that is visible in MAG data from all Enceladus flybys carried out
to date. Model-data comparisons for E3-E13 are presented. Besides, we discuss
Cassini magnetic field observations from the only two close flybys (16DI and 129DI) of
Saturn's icy satellite Dione which have been carried out so far. Data from 16DI show a
weak field perturbation in the upstream region, indicative of a tenuous atmosphere
around the satellite. We demonstrate that an atmospheric column density on the
order of 10^17/m2 would be required to sustain the observed field signature. The
detection of such an atmosphere may be correlated to the occurrence of a transient
radiation belt near Dione's L-shell at the time of 16DI. On the other hand, magnetic
field observations from the subsequent downstream encounter 129DI show no clear
evidence of an atmosphere, probably due to the flyby trajectory being
unsuitable
for the detection of the associated perturbations. Finally, we elaborate on the
possible existence of a highly asymmetric atmosphere around Rhea, leaving a
characteristic fingerprint in the magnetic field signatures observed during close flybys
of this moon.
MOP2011-P0009
Oral (Contributed)
Particle energization at Saturn
Paranicas, C. [1], E. Roussos [2], P. Kollmann [2], N. Krupp [2], J. Carbary [1], D.
Mitchell [1], T. Krimigis [1], B. Mauk [1] and G. Clark [3]
[1] JHU/APL, JHU/APL
[2] MPS, MPS
[3] SWRI, SWRI
Saturn's radiation belts have been shown to be substantially less intense than those of
Earth, Jupiter or Uranus.
This may be because the circumplanetary neutral gas torus
erodes the energy of energetic electrons through collisions and also limits the lifetimes
of ions of different species over wide energy ranges. For example, energetic protons
below about 100 keV undergo charge exchange in the neutral gas and can exit the
system as energetic neutral atoms.
For both electrons and protons in the tens to
hundreds of keV, the action of the gas torus makes the seed population for the
radiation belts less permanent.
But injections that initially energize these particles are
apparently sufficient to create belts even though there are strong losses.
Processes
such as stripping collisions of energetic neutrals do mitigate the loss of the seed
population to some extent. In this talk, we will look at the role of injections of both
electrons and protons in supplying the belts and whether these processes are
sufficient to reproduce the data.
MOP2011-P0015
Oral (Contributed)
An Atmospheric Vortex as the Driver of Saturn's Electromagnetic
Periodicities: 2. Magnetospheric and Ionospheric Responses
Kivelson, M.G.[1,2], X. Jia [2] and T.I. Gombosi [2]
[1] UCLA, Dept Earth and Space Sciences
[2] University of Michigan, Dept Atmospheric, Oceanic and Space Sciences
Using the output of a magnetohydrodynamic simulation that models nominal
southern summer conditions by imposing vortical flows in the southern ionosphere
(described in part 1 of this presentation), we show that the model reproduces
numerous features of the magnetosphere's periodic behavior.
We comment in
particular on the appearance of a rotating, nearly uniform perturbation field in the
equatorial plane inside of roughly 10 RS driven by a cam current system, rotating
azimuthal structure in the mass density at small radial distances and in the azimuthal
current density, strong localized field-aligned current out of the southern ionosphere
that intensifies as it rotates through the morning sector (where it can account for
observations of SKR rotation combined with localization of its most intense emissions).
Additional aspects of the responses include a local-time fixed asymmetric azimuthal
ring current, plasma sheet periodicities in the tail, and other observed features of the
magnetosphere.
hemisphere
Further runs are needed to establish the role of northern
perturbations
during
southern
summer.
We
argue
that
the
magnetosphere is remotely sensing structure that appears to be present in the high
latitude ionosphere.
MOP2011-P0022
Oral (Contributed)
Perpendicular Flow Separation in a Magnetized Counterstreaming
Plasma: Application to the Dust Plume of Enceladus
Jia, Y. [1], Y. Ma [1], C.T. Russell [1,2], G. Toth [3], T.I. Gombosi [3] and M.K. Dougherty
[4]
[1] Institute of Geophysics and Planetary Physics, University of California, Los Angeles
[2] Earth and Space Sciences, University of California, Los Angeles
[3] Space Physics Research Laboratory, Univerisity of Michigan
[4] Space and Atmospheric Physics G
The interaction of charged dust with a magnetized flowing plasma can be treated
with a multi-fluid MHD simulation. We examine the interaction of the corotating
Saturnian plasma with the charged-dust plume of Enceladus. The model produces
plasma deceleration with both positively and negatively charged dust. In addition,
the negatively charged dust causes plasma deflection in the direction of the motional
electric field and a kink in the magnetic field extending in the same direction.
Positively charged dust causes the opposite plasma deflection and the opposite
magnetic field bending. These results agree with the magnetic signatures observed
on Cassini plume flybys. The code has been tested on both subsonic and supersonic
interactions and is applicable to solar wind dust pickup, ICME interactions with dust
trails, cometary plasma pickup, active plasma releases such as the AMPTE barium
release as well as the Enceladus plume.
MOP2011-P0026
Oral (Contributed)
Periodicities in Saturn's Magnetosphere: An Example of Murphy's Law?
Vasyliunas, V.M.[1]
[1] -, Max-Planck-Institut fuer Sonnensystemforschung
Research on time variations with periods near 10 hours in the magnetosphere of
Saturn has been marked by a remarkable tenacity in interpreting observations in
terms of pre-existing concepts, together with an unprecedented tendency for each
new observation to knock down the present interpretation. When first observed, the
modulation of SKR emissions was interpreted as a rotating-beacon source, of a type
already familiar from Jupiter and usable to determine the planet's rotation period.
Shortly thereafter, observations from the Voyager 1 flyby showed that SKR was not a
rotating beacon but a strobe; a further result was that the SKR emitting region near
the planet is fixed in local time, so it does not rotate, either. Despite this, the SKR period
was treated as the rotation period of Saturn for nearly two decades, until new
observations showed that the period was variable on a scale (percent per year)
inconceivable for a rotating giant planet; the misleading terminology "radio rotation
period" for SKR persists to this day. The azimuthal asymmetry necessary if rotation is to
produce a periodic variation was assumed at first to be in Saturn's internal magnetic
field, which, however, has proved unique in being symmetric around the rotation axis.
Various rotating asymmetries in the magnetosphere have now been identified,
although there are only speculations and no viable theory as to the origin of them.
Just when the association of SKR pulses with a particular local-time location of the
magnetospheric asymmetric structure seemed to be reasonably confirmed, new
observations indicated a systematic and variable difference between the apparent
SKR periods in the northern and the southern hemispheres. To my mind, this rules out
magnetospheric asymmetry as a direct cause of SKR modulation and suggests that
atmospheric effects (some type of neutral-wind dynamo) may be more important.
MOP2011-P0027
Oral (Contributed)
Grapes from Saturn : <br> focus on Saturn's main ring of emission with
Cassini-UVIS
Grodent, D. [1], J. Gustin [1], J. G?rard [1], A. Radioti [1], B. Bonfond [1] and W.R.
Pryor [2]
[1] LPAP, Universite de Liege
[2] Science Department, Central Arizona College
During Cassini's spacecraft high latitude orbit 82, the onboard UVIS imaging
spectrograph obtained spatially resolved spectra of Saturn's auroral emissions.
On 26
August 2008, Cassini flew over Saturn's surface at an altitude less than 5 R S and
planetocentric sub-latitude higher than 55 deg. This unique vantage point provided
an unprecedented view of the northern hemisphere with a spatial resolution close to
200 km. The reconstructed images reveal that on that day, the main ring of emission
was far from uniform. We report the observation of two types of UV auroral
substructures at the location of the main ring of emission; bunches of spots and short
narrow arcs. The horizontal width of the narrowest arcs appears to be as small as 500
km across (0.5 deg of latitude) which is associated with the width of a source region of
1 to 2 RS in the equatorial plane. A series of 14 isolated quasi-corotating spots are
found to be arranged in a 'bunch of grapes' configuration near the noon sector. Each
'grain' or spot is characterized by a horizontal scale of ~2000 km which magnetically
maps to an equatorial source region of approximately 4 R S. Typical brightness of these
auroral features ranges from 1 to 30 kR. These small scale substructures are likely
associated with patterns of upward field aligned currents resulting from non-uniform
distribution of the plasma flow in the equatorial plane. We suggest that the bunch of
auroral UV spots that we observe in the northern ionosphere of Saturn might be
signatures of successive vortices triggered by Kelvin-Helmholtz waves, and travelling
tailward along the dayside magnetopause.
MOP2011-P0033
Oral (Contributed)
Jupiter's Radio Rotation Period: A 50-year Average
Higgins, C. [1], D. Solus [1], F. Reyes [2] and T. Carr [2]
[1] Middle Tennessee State University, Physics & Astronomy
[2] University of Florida, Astronomy
Using 50 years of continuous seasonal observations of Jupiter's decametric radio
emissions from 18-22 MHz collected at the University of Florida Radio Observatory
(UFRO), we calculate a new radio rotation period of Jupiter. The new period is the
weighted mean of 24 independent measurements where each independent
measurement is based on a 24-year average. Each measurement is found by
determining the drift of the histograms of probability of occurrence versus the System
III (1965) central meridian longitude (CML) over intervals of approximately 24, 36, and
48 years. This multiple 12-year average technique is employed to reduce the
uncertainty in the longitudes of the radio sources caused by Jupiter's 11.86 year orbit.
Our weighted mean is 9 hours 55 minutes 29.687 seconds, with a standard deviation of
the weighted mean of 0.003 seconds. This is a further refinement of the period
calculated by Higgins et al. (1997) shown by a reduced uncertainty. Our calculations
show a remarkably stable system. An upper limit of any radio rotation period drift is
discussed.
MOP2011-P0038
Oral (Contributed)
Evidence at Saturn of an Inner Magnetospheric Convection Pattern,
Fixed in Local Time
Thomsen, M.F.[1], R.L. Tokar [1], E. Roussos [2], M. Andriopoulou [2], C. Paranicas [3],
P. Kollmann [2] and C.S. Arridge [4]
[1] Space Science and Applications, Los Alamos National Laboratory
[2] n/a, Max-Planck Institute for Solar System Research
[3] Johns Hopkins University Applied Physics Laboratory, Johns Hopkins University Applied Physics
Laboratory
[4] Mullard Space Scien
We draw together several independent lines of evidence that suggest the existence
of an average local-time-fixed convection pattern in the inner magnetosphere of
Saturn.
The inferred convection pattern is such that magnetospheric particles
corotating and gradient/curvature-drifting around Saturn tend to drift radially
outward on the dawn side of the magnetosphere and radially inward on the dusk side.
The resulting drift orbits have an outward bulge at noon.
Evidence supporting the
existence of such a pattern includes 1) average plasma ion and electron
temperatures that are higher on the nightside than on the dayside; 2) average
energetic particle fluxes that are higher on the nightside than on the dayside; 3) the
tendency for satellite absorption signatures in the energetic particle population to lie
outwards of the satellite orbital radius on the dayside but inwards of it on the nightside;
and 4) day/night differences in the radial location of the charged-particle absorption
edge of the main rings.
The average electric field that would be needed to support
such a convection pattern is of a magnitude that is comparable to what has been
inferred from the energy dependence of the radial location of satellite absorption
signatures.
MOP2011-P0041
Oral (Contributed)
Io's Plasma Interaction with the Plasma Torus within the Jovian
Magnetosphere
Winglee, R. [1], E. Harnett [1] and J. Waldock [1]
[1] Univ. of Washington, Dept Earth and Space Sciences
Multi-fluid/Multi-Scale simulations are used to investigate the induced magnetosphere
around Io and the mass loading within the context of the global Jovian
magnetosphere. Long duration simulations have now been develop that show both
the small scale features around Io along with the extended features of Io's plasma
which is almost in co-rotation with the Jovian magnetic field. It is shown that because
of the strong magnetic field at Io, most of the outflow is launch along the field lines
and reaches latitudes well above Io's latitude. This plasma then convective drifts in the
azimuthal direction in addition to being convected towards the magnetic equator.
The amount of outflow from Io is strongly modified by its position within the torus and
this variable outflow leads to a variety of difference structures both along and across
the Io plasma torus.
The resultant density profile on average agrees well with the
average density profiles inferred for the Io plasma torus, but locally the density profile
can differ significantly from the average profiles. These variations produce changes in
the local current system around Io as well as losses from the torus to the Jovian
ionosphere and to the Jovian magnetosphere.
MOP2011-P0042
Oral (Contributed)
Periodicities in Saturn's ENA and their Correlation with SKR
Carbary, J. [1], D. Mitchell [1], P. Brandt [1], S. Krimigis [1] and D. Gurnett [2]
[1] Appied Physics Laboratory, Johns Hopkins University
[2] Dept of Physics and Astronomy, Universtiy of Iowa
Cassini orbits during days 200-366 in 2004 afforded an excellent opportunity to
continuously observe Saturn energetic neutral atom emissions from long range (>50
RS) on the dawn side.
Energetic hydrogen (25-55 keV) and oxygen (90-160 keV)
atom fluxes were projected onto the noon-midnight plane, corrected for travel time
from Saturn, averaged into half hour time bins and finally averaged into 60x40 RS
spatial bins.
The time profiles of these averages were then subjected to a Lomb
periodogram analysis.
The H periodogram exhibits a weak periodicity (SNR=9.1) with
a major peak at 10.78 hours and several minor peaks.
The O periodogram displays
strong periodicities (SNR=36.2) with a major peak at 10.78 hours and a secondary
peak at 10.61 hours, which coincide with the dual periods noted in the SKR.
A cross
correlation of the SKR signal with the ENA signals reveals that the H signal leads the SKR
by 1.1 hours, while the O signal leads the SKR by 2.6 hours.
ENA-SKR phasing will be discussed.
Implications for the
MOP2011-P0044
Oral (Contributed)
Moon-Planet and Exoplanet-Star Couplings: Common sub-Alfvenic
Interaction Mechanisms Throughout the Universe
Saur, J. [1], T. Grambusch [2] and S. Duling [1]
[1] Institute of Geophysics and Meteorology, University of Cologne
[2] Institute of Physis I, University of Cologne
Planetary bodies throughout the universe are generally exposed to the flow of
magnetized plasma. If the relative velocity between the plasma flow and the
planetary body is lower than the Alfven velocity, i.e. if the flow is sub-Alfvenic, then
momentum and energy can be transported in the upstream direction of the flow and
reach the parent planet or the parent star. Such coupling is observed at Io, Europa,
Ganymede, and Enceladus in form of auroral footprints and electron beams near the
satellites. But there is also observational evidence for footprints of extra-solar planets
on their central stars when the exoplanets are sufficiently close to their central stars. In
this presentation, we will compare the sub-Alfvenic electrodynamic coupling
mechanisms at the planetary moons of Jupiter, Saturn, and exoplanets. We will derive
expressions for the energetics of the interaction, which we use for comparison with the
observed luminosities of the footprints.
MOP2011-P0045
Oral (Contributed)
Natural Radio Emission of Jupiter as Interferences for Radar Investigations
of the Icy Satellites of Jupiter
Cecconi, B. [1], S. Hess [2], A. H?rique [3], M. Santovito [4], D. Santos-Costa [5], P.
Zarka [1], G. Alberti [4], D. Blankenship [6], J. Bougeret [1], L. Bruzzone [7] and W.
Kofman [3]
[1] LESIA, CNRS-Observatoire de Paris
[2] LATMOS, CNRS-UVSQ
[3] IPAG, CNRS-Univ. J. Fourier
[4] CORISTA, Univ. degli Studi di Napoli Federico II
[5] Space Science Department, SwRI
[6] Institute of Geophysics, Univ. Texas
[7] Dept. of Civil and Environment
Radar instruments are part of the core payload of the two Europa Jupiter System
Mission (EJSM) spacecraft: NASA-led Jupiter Europa Orbiter (JEO) and ESA-led Jupiter
Ganymede Orbiter (JGO). At this point of the project, several frequency bands are
under study for radar, which ranges between 5MHz and 50MHz. Part of this frequency
range overlaps with that of the natural Jovian radio emissions, which are very intense
in the decametric range, below 40 MHz. Radio observations above 40 MHz are free of
interferences, whereas below this threshold, careful observation strategies have to be
investigated. We present a review of spectral intensity, variability and sources of these
radio emissions. As the radio emission are strongly beamed, it is possible to model the
visibility of the radio emissions, as seen from the vicinity of Europa or Ganymede. We
have investigated Io-related radio emissions as well as radio emissions related to the
auroral oval. We also review the radiation belts synchrotron emission characteristics.
We present radio sources visibility products (dynamic spectra and radio source
location maps, on still frames or movies), which can be used for operation planning.
This study clearly shows that a deep understanding of the natural radio emissions at
Jupiter is necessary to prepare the future EJSM radar instrumentation. We show that
this radio noise has to be taken into account very early in the observation planning
and strategies for both JGO and JEO. We also point out possible synergies with RPW
(Radio and Plasma Waves) instrumentations.
MOP2011-P0046
Oral (Contributed)
Saturation of Cyclotron Maser Instability in Jupiter's Radiosources ?
Zarka, P. [1], B. Cecconi [1], L. David [1] and T. Garrigoux [1]
[1] Observatoire de Paris - CNRS, LESIA
The emission process for Jupiter's high latitude radio emissions isknown to be the
Cyclotron Maser Instability, which produces and amplifies radiation at the local
cyclotron frequency fce. Previous theoretical studies (e.. LeQueau, 1988) suggest that
the emission process might be saturated. Knowing if and at which level the Cyclotron
Maser instability saturates has never been achieved at an planet, although it is
believed that wave growth remains linear at Earth. Deermining if saturation occurs at
Jupiter is thus an interesting question, that may have implications for detection of
exoplanetary counterparts of Jupiter's magnetospheric radio emissions. We present
the analysis of waveform recordings of Jovian ? S-burst ? emission sampled at 80 MHz.
Saturation signatures are searched by several methods. They basically consist in
searching for waveform segments with maximum, nearly constant amplitude, from
elementary sources isolated though digital filtering.
MOP2011-P0053
Oral (Contributed)
A Magnetospheric Vortex as the Source of Periodicities in Saturn's
Magnetosphere
Khurana, K.K.[1]
[1] University of California at Los Angeles, Institute of Geophysics and Planetary Physics
The length of the days of planets lacking solid surfaces have traditionally been
obtained from the modulations of radio waves emanating from their auroral regions.
Saturn also emits intense radio waves called Saturn's Kilometric Radiation (SKR)
modulated by its rotation but with a period that is known to vary by about 1% over a
time scale of years. Recently, it was shown that the SKR emitted from the northern and
the southern hemispheres have slightly different modulation periods creating a
puzzling but persistent dual clock in the Saturn system.
<br> <br> In this work, we
show that the modulations of SKR emissions and many field and plasma parameters
are the manifestations of a massive (M > 10 8 kg) slow-moving (V < 1.5 km/s) two-cell
plasma convection system operating in the inner magnetosphere of Saturn that was
first proposed by Gurnett et al. (2007). We show that during the southern summer the
longer-period southern SKR emissions are exclusively excited by sources in the plasma
outflow region of the convection system which lags corotation to conserve angular
momentum. The two key components of Saturn's summer clock are the unequal
conductivities of the northern and the southern hemispheres from differences in solar
insolation and a plasma convection cycle that provides persistent memory to the
magnetosphere. We illustrate, how, various field and plasma parameters synchronize
themselves to Saturn's summer clock.
MOP2011-P0060
Oral (Contributed)
Model of the Jovian magnetic field topology constrained by the Io
auroral emissions
Hess, S. [1], B. Bonfond [2], D. Grodent [2] and P. Zarka [3]
[1] Universit? Versailles St Quentin - CNRS, LATMOS
[2] Universit? de Li?ge, LPAP
[3] Observatoire de Paris, LESIA
The determination of the internal magnetic field of Jupiter has been the object of
many studies and publications. These models have been computed from the
Pioneer,Voyager, and Ulysses measurements. Some models also use the position of
the Io footprints as a constraint: the magnetic field lines mapping to the footprints
must have their origins along Io's orbit. The use of this latter constraint to determine the
internal magnetic field models greatly improved the modeling of the auroral emissions,
in particular the radio ones, which strongly depends on the magnetic field geometry.
This constraint is, however, not sufficient for allowing a completely accurate modeling.
The fact that the footprint field line should map to a longitude close to Io's was not
used, so that the azimuthal component of the magnetic field could not be precisely
constrained. Moreover, a recent study showed the presence of a magnetic anomaly
in the northern hemisphere, which has never been included in any spherical harmonic
decomposition of the internal magnetic field. We compute a decomposition of the
Jovian internal magnetic field into spherical harmonics, which allows for a more
accurate mapping of the magnetic field lines crossing Io, Europa, and Ganymede
orbits to the satellite footprints observed in UV. This model, named VIPAL, is mostly
constrained by the Io footprint positions, including the longitudinal constraint, and
normalized by the Voyager and Pioneer magnetic field measurements. We show that
the surface magnetic fields predicted by our model are more consistent with the
observed frequencies of the Jovian radio emissions than those predicted by previous
models.
MOP2011-P0069
Oral (Contributed)
Electrons at Saturn's moons: selected CAPS-ELS results
Coates, A. [1,2], G. Jones [1,2], C. Arridge [1,2], A. Wellbrock [1,2], G. Lewis [1,2], D.
Young [3], F. Crary [3], H. Waite [3], B. Johnson [4] and T. Hill [5]
[1] University College London, Mullard Space Science Laboratory
[2] UCL/Birkbeck, Centre for Planetary Sciences
[3] SwRI, Space Science and Engineering
[4] Materials Science and Engineering, University of Virginia
[5] Physics and Astronomy, Rice Universit
Saturn's moons provide a fascinating laboratory for studying plasma interactions with
unmagnetized objects. A range of interaction types occur, including Titan with its
dense atmosphere, Enceladus with its plume and Rhea with its weak atmosphere.
Here we present several highlights of the CAPS results emphasizing those from the ELS,
including observations of negative ions at Titan, Enceladus and Rhea, and
photoelectron observations at Titan. We also discuss prospects for other outer solar
system moons.
MOP2011-P0087
Oral (Contributed)
Plasma-induced Sputtering and Heating of Titan's Atmosphere
Tucker, O.J.[1] and R.E. Johnson [1]
[1] University of Virginia, Engineering Physiscs
Following numerous passes of Cassini through Titan's upper atmosphere there appears
to be new evidence for plasma-induced heating and sputtering of Titan's upper
atmosphere (Westlake et al. 2011). Using a Direct Simulation Monte Carlo model of
Titan's upper and recent estimates on the charged particle flux, we re-examine the
effect of the incident plasma ions on the escape rate and the thermal structure of
Titan's upper atmosphere.
MOP2011-P0088
Oral (Contributed)
Simultaneous infrared and ultraviolet observations of Saturn's aurora using
Cassini VIMS and UVIS
Melin, H. [1,2], T. Stallard [1], S. Miller [3], J. Gustin [4], M. Galand [5], S.V. Badman [6],
W. Pryor [7,2], J. O'Donoghue [1], R.H. Brown [8] and K.H. Baines [9]
[1] Physics & Astronomy, University of Leicester
[2] Planetary & Space Science Division, Space Environment Technologies
[3] Physics & Astronomy, University College London
[4] Laboratoire de Physique atmosph?rique et plan?taire, University of Liege
[5] Phy
With Cassini VIMS and UVIS providing wavelength coverage in the infrared and the
ultraviolet respectively, it is possible to observe the aurora of Saturn in these bands
with both spatial and temporal simultaneity. Here, the very different operational
modes of the instruments are described, governing what degree of true simultaneity
can be achieved.
Simultaneous VIMS and UVIS observations from 2008-254 were
taken when Cassini was only 6 RS from Saturn, giving a spatial resolution of 300 km per
mrad. This pre-dawn observation shows three arcs, all with different H, H2 and H3+
emission characteristics. One is seen clearly in all three species, one is seen mainly in H
and one is seen mainly in H2 and H3+. These differences are likely due to different
particle precipitation energies.
MOP2011-P0097
Oral (Contributed)
Cassini Data Comparison with Hybrid Model: Role of Oxygen Ions in Titan's
Interaction
Sillanp??, I. [1], D.T. Young [1], F. Crary [1], M. Thomsen [2], D. Reisenfeld [3], J.
Wahlund [4], C. Bertucci [5], E. Kallio [6], R. Jarvinen [6] and P. Janhunen [6]
[1] Space Science and Engineering, Southwest Research Institute
[2] -, Los Alamos National Laboratory
[3] -, University of Montana
[4] Uppsala division, Swedish Institute of Space Physics
[5] -, Institute for Astronomy and Space Physics
[6] Earth Observat
During the Cassini Titan flyby on 2 July 2006 (T15), Titan was surrounded by a
magnetospheric plasma flow with density about 0.1 cm-3 as measured by Cassini
Plasma Spectrometer (CAPS). A very low fraction of water-group ions (O+) was
detected in the flow dominated by hydrogen ions. We show that Titan's plasma
interaction can be highly sensitive to the small fraction of oxygen ions in the
magnetospheric flow. The ion quantities of the magnetospheric flow during the flyby
were obtained from numerical moments calculated from the CAPS measurements;
the
average
ambient
magnetic
field
was
determined
using
the
Cassini
magnetometer data. We simulated the flyby using a global hybrid model; the
water-group abundance in the flow was varied in three simulation runs. Based on the
simulation results the oxygen content has especially notable effect on the extent of
Titan's
induced
magnetosphere.
A
multi-instrument
analysis
was
performed
comparing with the simulations, whereby a comprehensive picture of the plasma
properties around Titan during this flyby was obtained. Comparisons between the
hybrid model simulations and Cassini measurements during the flyby point towards O +
density in the undisturbed magnetospheric flow having been around 0.008 cm -3,
which would have accounted for one half of the dynamic pressure of the flow.
MOP2011-P0101
Oral (Contributed)
Saturn's Magnetospheric Period.
Rymer, A. [1], D. Mitchell [1], T. Hill [2], E. Kronberg [3] and N. Krupp [3]
[1] Space Physics Group, JHU/APL
[2] Department of Physics and Astronomy, Rice
[3] Deparment of Planets and Comets, MPS
[4] Deparment of Planets and Comets, MPS
At Jupiter, in addition to strong clock-like modulation at the planetary spin rate, there
is also a quasi-periodic 2-3 day modulation associated with plasma bursts, auroral
brightening
and
magnetospheric
reconfiguration
events.
The
quasi-periodic
modulation has been associated with a characteristic (internally driven) global
magnetospheric mass-loading and unloading rate [Kronberg et al., 2007 JGR].
The
process is rather analogous to the filling and unfilling of a Japanese shishi-odoshi or
'deer scarer' fountain. Mass loading at Saturn is intrinsically less than that of Jupiter,
however Vayliunas (2008) showed that when expressed in dimensionless units (for
example as a function of magnetospheric cavity size) Saturn is ~40-60 times more
mass loaded than Jupiter. The equivalent mass unloading timescale at Saturn to the
2-3 day period at Jupiter is therefore expected to be ~8-12 hours.
We present our
calculations and discuss in the context of rotationally modulated phenomena at
Saturn.
MOP2011-P0106
Oral (Contributed)
Hot Plasma Characteristics in the Outer Magnetosphere of Saturn
Kane, M. [1], D. Mitchell [2], J. Carbary [2] and S. Krimigis [2]
[1] Space Physics, Harford Research Institute
[2] Applied Physics Laboratory, Johns Hopkins University
The dominant structural feature of Saturn's magnetosphere is the presence of an
extensive magnetodisk partially rotating with the planet.
This structure interacts with
the magnetopause, transporting magnetospheric particles and their momentum into
the solar wind in the magnetosheath. In the dayside, the extent of the disk is clearly
limited by the magnetopause boundary. In the nightside, however, the structure is
stretched by centrifugal force deep into the tail.
While the motion of this structure is
predominantly rotational, there is a significant radial expansion.
rates in the nightside are derived and binned in local time.
Radial transport
The rates act as a
constraint on the size of this structure in the nightside if one assumes distant nightside
plasma is not recirculated around the dayside.
They also would be affected by the
extent of plasma detachment in the nightside.
At large distances, in a deep tail orbit
of Cassini, hot plasma is depleted which could indicate that an outer edge of the disk
was traversed.
When scaled to the Jovian magnetosphere, this distance is consistent
with the point where the Voyager 2 spacecraft stopped sensing plasma sheet
crossings.
We examine in detail the dusk and dawn low latitude flanks in the vicinity
of the magnetopause crossings.
magnetosphere.
We find evidence of tailward transport within the
There is a significant population of hot magnetospheric oxygen
ions in the magnetosheath.
Outer magnetodisk [nightside] plasma must be
transported inward in the pre-dawn region to recirculate in the dayside, but we find
radial transport is outward here.
At the dusk flank, the radial transport reveals the
extent of an expected region of rapid expansion of the disk near the dusk terminator.
We present analysis from recent dusk equatorial orbits near the dusk magnetopause.
MOP2011-P0110
Oral (Contributed)
Saturn's 10.8 Hour Periodicity - Relationship Between Cold, Sub-corotating
Plasma and Hot Ring Current Particles
Mitchell, D. [1], P. Brandt [1], A. Rymer [1] and J. Carbary [1]
[1] JHU/APL, Space
It is well established that beyond about 3 Rs, the plasma in Saturn's magnetosphere
has an azimuthal convection velocity substantially below the velocity that would be
consistent with rotation of the magnetosphere at the period determined by Saturn
Kilometric Radiation (SKR).
Whereas SKR is a fairly high latitude phenomenon, there
are many magnetospheric parameters (magnetic field perturbations, cold plasma
density between 3 and 5 Rs, ENA emissions, energetic electrons, cold plasma density
in the middle and outer magnetosphere) that exhibit periodic behavior at periods
indistinguishable from the SKR period.
Reconciling these observations with the
substantially longer cold plasma (magnetospheric) rotation period remains a
challenge.
The observed periodicities at the SKR period act like a wave propagating
'downstream' through the more slowly moving cold plasma. In this paper, we discuss
the possible mechanisms for the communication of this wave throughout most of the
magnetosphere, with particular attention to the role of hot (10's to 100's of keV) ions
and warm (10's to 1000's of eV) electrons in distributing the signal over broad radial
distances in the magnetosphere, as well as communicating the signal between the
magnetosphre and the ionosphere.
MOP2011-P0111
Oral (Contributed)
In Search for a Self-consistent Hypothesis for Saturn's Periodicities:
Shielding Effects of a Partial Ring Current
brandt, p.c.[1], d.g. mitchell [1] and Y. Ebihara [2]
[1] Space Department, JHU/APL
[2] RISH, Kyoto University
A global hypothesis is emerging from several efforts in which plasmoids are released
quasi-periodically down the tail, leading to the periodic signatures of energetic
particles, SKR and magnetic field perturbations. Arguments have been raised that a
natural period of the plasmoid release is not sufficient for maintaining the Saturn
"clock" and therefore ionospheric or magnetospheric asymmetries have been
prescribed to explain the clock-like behavior. Recent work by Jia et al. [MAPS Meeting,
2011] using a single-fluid MHD model, demonstrated remarkable agreement with the
observed periodic magnetic field perturbations by prescribing a pair of ionospheric
vortices, or, equivalently, a pair of field-aligned currents (FACs), rotating at the SKR
period to enforce an azimuthal asymmetry in the cold plasma that leads to plasmoid
release at that same rotation rate.
In the context of this global hypothesis, we
investigate how this prescribed FAC pair can be produced and maintained. Based on
what we know from the terrestrial magnetosphere we discuss how a partial ring
current (PRC) produces a "shielding" electric field through its closure through the
finitely conducting ionosphere. At Earth, this shielding field has long been known to
cause visible effects in Earth's plasmasphere. Given the observations and modeling of
the terrestrial phenomena, we seek to transfer this knowledge to the Saturnian
magnetosphere. At Saturn, the PRC-driven FACs flows out of the ionosphere at the
western edge of the PRC, and into the ionosphere at the eastern edge. This sets up a
west ward electric field that spreads to lower latitudes and induces an outward
motion of the cold plasma, producing a bulge that propagates azimuthally through
the cold plasma together with the rotating PRC shielding field. Even though the cold
plasma sub-corotates, the energetic particle drift period, and hence the shielding
electric field rotation period, is also between 10-11 h. The resulting bulge in the cold
plasma, and perhaps some of the field is then responsible for triggering the next
plasmoid release. We present INCA observations that clearly show how energetic
particle injections drift around the planet and how a new night side injection appears
when the old injection reaches the night side again. We also discuss the formation of
interhemispheric FACs as reported by Andrews et al. [2010], their relation to the PRC
and their seasonal dependence.
MOP2011-P0115
Oral (Contributed)
Plasma Populations in Saturn's High Latitude Magnetosphere and their
Mapping to the Ionosphere
Arridge, C. [1,2], N. Achilleos [3,2], S. Badman [4], E. Bunce [5], P. Schippers [6], D.
Talboys [5], A. Coates [1,2] and M. Dougherty [7]
[1] Mullard Space Science Laboratory, University College London
[2] The Centre for Planetary Sciences, UCL/Birkbeck
[3] Department of Physics and Astronomy, University College London
[4] Institute of Space and Astronautical Science, JAXA
[5] Department of
The Cassini spacecraft has now made a large number of highly inclined orbits of the
magnetosphere
providing
the
opportunity
to
sample
the
high
latitude
magnetosphere. Numerous plasma populations have been observed in this region of
Saturn's magnetosphere, including evidence for the polar cusp, polar cap, plasma
sheet, and energised populations associated with field-aligned electrons and
kilometric radio emissions. In this paper we present a statistical survey of these
populations. The observed populations are mapped down to the ionosphere to
establish the average spatial distribution of various populations at high latitudes. These
populations are also compared with observed field-aligned currents and average
patterns of auroral emissions.
MOP2011-P0118
Oral (Contributed)
Jovian anomalous continuum radiation
Ye, S. [1], D.A. Gurnett [1], J.D. Menietti [1], W.S. Kurth [1] and G. Fischer [2]
[1] Department of Physics and Astronomy, The University of Iowa
[2] Space Research Institute, Austrian Academy of Sciences
Jovian anomalous continuum is an electromagnetic radiation near 10 kHz that can
escape from Jupiter's magnetosphere to the solar wind. The lower frequency cutoff of
the anomalous continuum is found to be related to the plasma frequency in the
magnetosheath of Jupiter, which is a function of solar wind density and the solar
zenith angle. One likely source of the Jovian anomalous continuum is the
quasi-periodic (QP) bursts that are generated in the inner magnetosphere of Jupiter.
While the lower frequency part of the QP bursts is trapped in the Jovian
magnetosphere, the higher frequency part can propagate through the Jovian
magnetosheath and, depending on the frequency, escape to the solar wind at
different solar zenith angles. The frequency dispersion of the anomalous continuum
originates from the slow group velocity of the waves as they propagate near local
plasma frequency in the magnetosheath. Jovian anomalous continuum radiation
was consistently observed by Cassini RPWS for more than two years after the Jupiter
flyby, which means the radiation can be detected as far as 5 AU away from Jupiter.
Rotational modulation analysis shows that the emission is modulated like a clock at
the system III period of Jupiter. The observation of the Jovian anomalous continuum
can be used as a remote diagnosis of the solar wind conditions at Jupiter.
MOP2011-P0121
Oral (Contributed)
Hybrid Simulations of the Callisto - Magnetosphere Interaction
Barabash, S. [1] and M. Holmstr?m [1]
[1] Solar System Physics program, Swedish Institute of Space Physics
The simulations of the Callisto - magnetosphere interaction is important (1) to
understand the origin of the magnetic field perturbations recorded by Galileo
(Khurana, 1998) potentially related to the subsurface ocean, and (2) to model the
plasma environment at this moon in preparation for the coming Jupiter system mission.
The airless non-magnetic Callisto is just a factor of 1.4 larger than the Moon. Therefore,
global hybrid models (particle ions, fluid mass-less electrons) simulating the Moon solar wind interaction may be readily applied to investigate the Callisto magnetospheric interactions provided the near - Earth solar wind parameters are
replaced by the ones corresponding to the Jovian conditions. We conducted runs of
such a model assuming the "solar wind" ions have the mass/charge equal to 16, the
temperature 45 eV, the density 0.5 1/cc, and the magnetic field equals to the
magnetospheric field. In these initial simulations we assumed the obstacle (Callisto) to
be fully non-conductive to simplify the boundary conditions. The first runs demonstrate
that the model used is capable of handling satisfactory the plasma conditions around
this satellite.
MOP2011-P0124
Oral (Contributed)
Titan's interaction with Saturn's magnetosphere: Plasma flow and
composition observed by Cassini/CAPS
Crary, F. [1], I. Silanpaa [1], M. Thomsen [2] and R. Tokar [2]
[1] Space Science Department, Space ScienceSouthwest Research Institute
[2] Space and Atmospheric Sciences Group, Los Alamos National Laboratory
Beginning in with Cassini's T63 Titan encounter, in late 2009, the spacecraft has made
five encounters which were optimized for thermal plasma measurements by the CAPS
instrument, and two which were a compromise between CAPS and radio science
gravity experiments. On previous encounter, pointing issues frequently limited
calculations of ion properties such as flow velocity or density, and typically produced
fragmentary profiles of these quantities. Seven of the Cassini encounters since T63
allow more complete and reliable determinations of the ion properties extending from
closest approach out to tens of Titan radii. We present these results and compare
them to models of the Titan interaction.
MOP2011-P0126
Oral (Contributed)
The Io Plasma Torus During the Cassini Flyby of Jupiter
Steffl, A.J.[1] and A.B. Shinn [1]
[1] Southwest Research Institute, Department of Space Studies
During the Cassini spacecraft's flyby of Jupiter (October 2000 through March 2001) the
Ultraviolet Imaging Spectrograph (UVIS) made extensive observations of the Io
plasma torus. The sensitivity, resolution, and imaging capabilities of UVIS coupled with
the temporal coverage of the observations make this a particularly rich data set.
Previous analysis and modeling has focused on a 45-day period from 1 October 2000
to 14 November 2000. This work has found a months-long change in the overall
ionization state of the torus, attributable to a factor of ~4 change in the amount of
neutral material supplied to the torus; persistent, nearly sinusoidal azimuthal variations
in torus ionization state with a rotation period longer than System III (i.e. System IV);
and modulation of the amplitude of these azimuthal variations by their position in
System III longitude. Here, we present the results from our efforts to analyze and model
UVIS data from 15 November 2000 to 17 March 2001 and place them within the
context of recent work on the Io plasma torus
MOP2011-P0127
Oral (Contributed)
Charged nanograins in the Enceladus plume
Hill, T. [1], R. Baragiola [2], A. Coates [3], F. Crary [4], M. Horanyi [5], R. Johnson [2], G.
Jones [3], G. Lewis [3], D. Mitchell [6], M. Thomsen [7], R. Tokar [7], J. Wahlund [8], R.
Wilson [5] and D. Young [4]
[1] Physics and Astronomy, Rice University
[2] Engineering Physics, Univ. Virginia
[3] MSSL, Univ. College London
[4] Space Science & Engineering, SWRI
[5] LASP, Univ. Colorado
[6] APL, Johns Hopkins Univ.
[7] Space Science & Applications, LANL
[8] ?ngstr
During the three Cassini encounters with the Enceladus plume for which the Cassini
Plasma Spectrometer had ram viewing, CAPS detected a cold but dense population
of heavy charged particles having mass-to-charge ratios up to the maximum
detectable by CAPS (~ 10^4 amu/e).
These particles are interpreted as singly
charged nanometer-sized water-ice grains (G. Jones et al., GRL, 2009).
Although
they are detected with both negative and positive net charges, the former greatly
outnumber the latter, at least in the M/Q range accessible to CAPS.
On at least one
encounter (E3, March 2008), we infer a net negative charge density ~ 1000 e/cm^3
for nanograins, far exceeding the ambient plasma number density, but less than the
net positive charge density inferred from the RPWS Langmuir probe data during the
same plume encounter (M. Shafiq et al., PSS, 2011).
Comparison of the CAPS
datasets from the three available encounters is consistent with the idea that the
nanograins leave the surface vents largely uncharged, but become increasingly
negatively charged by plasma electron impact as they move farther from the satellite.
In any case, nanograins clearly provide a potent source of magnetospheric plasma in
the near vicinity of Enceladus.
MOP2011-P0129
Oral (Contributed)
Discovery of an Unidentified Emission Band in Io's Eclipse Spectrum
Trafton, L.M.[1], C.H. Moore [2], D.B. Goldstein [2] and P.L. Varghese [2]
[1] University of Texas at Austin, Department of Astronomy
[2] University of Texas at Austin, Department of Aerospace Engineering and Engineering
Mechanics
Processing of HST/STIS spectra obtained during the 1999 Io-Galileo Campaign has
revealed previously unreported spectral band emission from 4100 to 5700 A that may
extend to longer wavelengths. This emission was detected in two consecutive CCD
exposures of Io's whole disk taken in early umbral eclipse during Aug 7, 1999, using
grating G430L. This grating has a dispersion 2.73 A/pixel and the effective spectral
resolution was 44 A, assuming uniform emission over Io's disk. The spectrum persists
when extracted from each half of Io's disk separately; and when extracted from each
of the two tandem eclipse exposures. The spectrum is not present in Jupiter's
scattered background. Fringing in the detector image was excluded as a source.
<br> <br> This long wavelength emission does not agree with Monte Carlo simulations
of Io's electron-excited SO2 and S2 emission. However, the intensity is consistent with
Galileo and Cassini images taken through filters that span this wavelength range,
which show evidence of emission on Io's night side not associated with SO 2 in the
volcanic plumes (Geissler et al. 1999, 2004). The regular emission features appear to
be spread too far apart to be rotational, excluding such diatomic molecules such as
NaK in the ground electronic state. They are more likely to be vibrational excitations,
indicating an unidentified electronically excited species. <br> <br> Geissler et al.
Science 285, 870, 1999; Icarus 172, 127, 2004
MOP2011-P0130
Oral (Contributed)
Plasma-Surface Interactions at the Icy Saturnian Moons: UV Surface
Effects
Hendrix, A.R.[1], T.A. Cassidy [1] and P. Chris [2]
[1] Caltech, JPL
[2] JHU, APL
The Saturnian system is a complicated mix of neutrals, icy E-ring grains, moons, cold
plasma and energetic particles. The interactions between these populations produce
observable effects on the surfaces on the icy moons. The ultraviolet is a key place to
look for these weathering fingerprints, as just the uppermost layers of the optical
surface are probed. Furthermore, the ultraviolet is a good spectral regime in which to
look for radiation products such as H2O2. We study spectral and spatial patterns on the
icy moons of Saturn using data from Cassini's Ultraviolet Imaging Spectrograph (UVIS)
and investigate their links to plasma interactions with the surface, and other exogenic
processes.
MOP2011-P0134
Oral (Contributed)
Dawn-Dusk Oscillation of Jupiter's Io Torus and the Vasyliunas E-V Theorem
Dessler, A. [1]
[1] Texas A and M, Atmospheric Science
It is commonly accepted that the dawn-dusk asymmetry and System III motion of Io's
plasma torus are explained by an electric field created by tailward plasma flow (Ref
1).
The electric-field-causation hypothesis may explain the persistent dawn-dusk
offsets, but it is inadequate to account for the observed torus
oscillation.
Specifically, the dawn and dusk torus ribbons oscillate in the same direction, nearly
rigidly. The ribbons, when either is near λIII = 110 deg, are observed to be farthest
from Jupiter1.
The E-field that might account for this System III oscillation phase
requires an inexplicably unique location for its generation. The futility of the E-field
hypothesis in explaining this oscillation is made obvious by the E-V theorem2, which
demonstrates that electric fields in magnetospheres are a result of plasma motion, not
their cause.
The E-V theorem also points to a solution: viz, a mechanical force, local
to the torus, that causes the oscillatory motion.
Centrifugal force is such a driver. All
that is required to explain the observed oscillation of the torus is a means of System III
modulation of tailward flow of plasma from the torus.<br> The needed modulation
mechanism is provided by the magnetic anomaly discovered and described by
Grodent et al3.
This anomaly comprises a previously unknown weak-field region in
Jupiter's northern hemisphere in the vicinity of λIII = 110 deg.
this anomaly maps to a region slightly beyond the torus.
The magnetic field from
Such an anomaly was (sort
of) anticipated by the magnetic-anomaly model in order to explain the System III
modulated phenomena that define the active sector (for a description of the
magnetic-anomaly model and active sector, see Chap. 10, Physics of the Jovian
Magnetosphere and Fig. 10-10).
The outflow is impounded at the anomaly because
ionospheric conductivity varies as 1/B, which causes the ionospheric magnetic field to
be more resistant to slippage.
Thus the anomaly locally impedes outflow of torus
plasma so torus outflow should be small around λIII = 110.
This model is consistent with
the observed torus oscillation.<br>1. Dessler, A.J. and B.R. Sandel, System III variations
in apparent distance of Io plasma torus from Jupiter, GRL 19, 2099, 1992 and GRL 20,
2489, 1993<br>2. Vasyliunas, V.M., Electric Field and Plasma Flow: What Drives What?,
GRL, 28, 2177, 2001<br>3. Grodent, D. et al, Auroral evidence of a localized magnetic
anomaly in Jupiter's northern hemisphere, JGR, 113, 2008
MOP2011-P0016
Oral (Contributed)
An Atmospheric Vortex as the Driver of Saturn's Electromagnetic
Periodicities: 1. Global Simulation
Jia, X. [1], M.G. Kivelson [1,2] and T.I. Gombosi [1]
[1] University of Michigan, Dept. of Atmospheric, Oceanic and Space Sciences
[2] UCLA, IGPP
Properties of Saturn's magnetospheric plasma, magnetic field and radio emissions
vary at a ~10.7 hour period, close to the period of planetary rotation with drifts of ~1%
per year. Identifying the source of the periodicity has proved challenging. The
ionosphere/thermosphere/upper-atmosphere, with low enough inertia to allow drift
and high enough inertia to maintain phase coherence, is a plausible source region.
Ionospheric properties affect the global magnetosphere most strongly by generating
field-aligned currents, and vortical flows in the ionosphere are an effective source of
such currents. Here, we use a global MHD simulation to investigate the response of the
coupled magnetosphere-ionosphere to a flow vortex fixed in the rotating southern
ionosphere/thermosphere. We find that the response of the magnetosphere to the
imposed flow anomaly produces a host of magnetospheric phenomena that have
been observed during southern summer. In this presentation, we will introduce the
basics of the global MHD simulation and the flow vortex model, followed by
discussions on simulation results regarding the global magnetospheric response to the
imposed ionospheric vortex. We note that the specific form of the vortex used is not
central to the analysis and a single vortex would provide the required symmetry
inferred from magnetospheric observations.
MOP2011-P0063
Oral (Contributed)
The MI-coupling in global simulations of the Jovian and Kronian
magnetospheres
Chan?, E. [1], J. Saur [1] and S. Poedts [2]
[1] University of Cologne, Institut f?r Geophysik und Meteorologie
[2] K.U.Leuven, Centrum voor Plasma-Astrofysica
We present a new model to study Jupiter's and Saturn's magnetosphere and how
they interact with the solar wind. In our model, the magnetosphere-ionosphere
coupling is consistently modeled by introducing ion-neutral collisions in the MHD
equations inside the simulation domain in an extended ionosphere located above
the inner boundary. In addition, the mass-loading caused by Io or Enceladus is
introduced in a axi-symmetric toroidal region where a ionization source term is added
to the MHD equations. With this model, two key parameters of the giant planets
magnetospheres can be controlled: namely the ionospheric conductivity and the
mass-loading associated with Io or Enceladus.
<BR><BR>
Our model was
extensively tested and the results were compared with measurements and analytical
models. For instance, for simulations of Jupiter's magnetosphere, the position of the
corotation break-down is in agreement with the model of Hill (1979). As expected by
theory, in our simulations, the position of the corotation break-down maps to the main
auroral emission. Comparing this auroral emission for different simulations, we show
that both the position of the corotation break-down as well as the location of the
magnetopause influence the shape and the luminosity of the main oval. In our
simulations, the azimuthal velocity profiles are very similar to the results obtained with
analytical models (e.g.?Saur?et?al.,?2004) and do not show spurious super-corotation
(as often seen in global MHD simulations of Jupiter's magnetosphere). In our
ionosphere, the current systems are closed inside the simulation domain by
ionospheric Pedersen and Hall currents produced by ion-neutral collisions: no current
is lost or gained through the boundary. The total current flowing through the
ionosphere (39.6?MA) agrees with estimates from measurements and analytical
models.
MOP2011-P0067
Oral (Contributed)
Inside the Jupiter Main Auroral Emissions: Flares, Spots, Arc...and Satellite
Footprints?
Bonfond, B. [1], M.F. Vogt [2], M. Yoneda [3], J. G?rard [1], D. Grodent [1], A. Radioti
[1], J. Gustin [1], T. Stallard [4] and J.T. Clarke [5]
[1] LPAP, University of Li?ge
[2] ESS, University of California, Los Angeles
[3] PPARC, Tohoku University
[4] Department of Physics & Astronomy, University of Leicester
[5] Center for Space Physics, Boston University
FUV auroral emissions located poleward of the main auroral "oval" are the most
dynamical part of the Jovian aurora, but also the most poorly understood. The
morphology and the dynamics of these emissions are extremely variable, ranging
from long arcs to tiny spots and
with evolution timescales ranging from tens of
seconds to several hours. Here we present recent analysis of the morphology, motion
and magnetospheric sources of three parts of the Jovian polar aurora: polar flares,
polar arcs and more surprisingly, spots associated to the Ganymede footprint.
Among this zoo of behaviors are the polar flares, which are dramatic but localized
enhancements of brightness. Recent Hubble Space Telescope observations of the
southern hemisphere demonstrated that these flares can re-occur quasi-periodically
every 2-3 minutes. This timescale had previously been observed as a flux transfer
events (FTEs) recurrence delay, in radio "type-III" bursts or in relativistic electron bursts.
Using a novel magnetic mapping model, we show that these flares could map either
to the outer dayside-duskside magnetosphere or to the magnetopause in the same
local-time sector and thus could be associated with pulsed reconnection.
Sometimes, the duskside polar region sometimes shows arcs that are parallel to, but
poleward of the
main oval arc. Here we show how they could be related to
magnetic signatures previously observed by the Ulysses spacecraft. We also discuss
how internal or external parameters could control their occurrence.
Moreover, we
demonstrate that the main emission (ME) can sometimes migrate equatorward in
such a way that the Ganymede footprint, which usually stands outside the ME, can
accidentally find itself inside the arc. This and other evidences contribute to the
suggestion that internal processes cause major changes in the current sheet.
MOP2011-P0068
Oral (Contributed)
The multiple spots of the Ganymede footprint
Bonfond, B. [1], S. Hess [2], D. Grodent [1], J. G?rard [1], J. Gustin [1], A. Radioti [1]
and J.T. Clarke [3]
[1] LPAP, University of Li?ge
[2] LATMOS, Universite Versailles-St Quentin - CNRS
[3] Center for Space Physics, Boston University
Satellite footprints are the auroral signature of the electromagnetic interactions
between satellites and their parent planet's magnetosphere. The footprints of Io,
Europa, Ganymede and more recently of Enceladus have been identified so far.
Moreover, the Io footprint has been shown to be formed of several spots, some being
related to Alfv?n waves directly propagating from Io to the Jovian poles, some being
related to Alfv?n waves reflected on the density gradient at the plasma torus
boundary. A third kind of spot has been recently attributed to trans-hemispheric
electron beams, i.e. electrons accelerated upward in one hemisphere but finally
precipitating in the opposite hemisphere. Here we show for the first time that the
Ganymede footprint is also formed of at least two spots. We analyze the relative
motion of this couple of spot in order to determine the processes generating them.
MOP2011-P0086
Oral (Contributed)
Identification of field-aligned electric current systems in Saturn's inner
magnetosphere
Schippers, P. [1], N. Andr? [2], G.R. Lewis [3], A.J. Coates [3], D.A. Gurnett [1] and
A.M. Persoon [1]
[1] University of Iowa, Department of Physics and Astronomy
[2] IRAP, CNRS/Universit? Toulouse III
[3] MSSL, University College of London
Using a statistics based on all the near-equatorial orbits of Cassini, we derive
averaged directional energy spectrograms for the North and the South hemispheres
(respectively positive and negative latitudes) separately. Inside Lshell~5, we observe a
pancake thermal population and a field-aligned cold (a few eV) electron population.
Out of Lshell~8, we observe a field-aligned warm population (10-100 eV) and an
energetic suprathermal electron population (1-10keV). The comparison of the
electron flux in the downward (from the equatorial plane) and the upward (towards
the equatorial plane) in both hemispheres highlight a net flux of downgoing electron
flux at Lshell~ 4-5, a net flux of upgoing electron flux at Lshell~8, and a net flux of
electron flux going from the Southern to the northern ionosphere at Lshell~10 and
similar features but less intense up to Lshell~18. We deduce that the observed
asymmetry of the parallel electron flux inside Lshell~9 is due to the presence of the
magnetosphere-ionosphere coupling current system enforcing the corotation in
Saturn's inner magnetosphere. The field-aligned currents outside Lshell~10 may be
consistent with an inter-hemispheric field-aligned current system in the 10-18 Lshell
range.
MOP2011-P0093
Oral (Contributed)
A statistical study of kilometric radiation fine structure striations observed
at Jupiter and Saturn
Kopf, A. [1,2] and D. Gurnett [1]
[1] Physics & Astronomy, University of Iowa
[2] Astronomy, University of Florida
The Cassini spacecraft, currently in orbit around Saturn, carries the Radio and Plasma
Wave Science (RPWS) investigation, which measures several different types of radio
emission from the local plasma environment at frequencies up to 16 MHz.
One such
type of emission is Saturn Kilometric Radiation (SKR), which is generally observed from
a few tens of kHz up to about 1 MHz.
One RPWS receiver, the Wideband Receiver, is
capable of making measurements of the fine structure that makes up the SKR
emission.
These data have revealed narrow negative-sloping striations with durations
of a few to about ten seconds, observed generally between 30-80 kHz. In addition,
while en route to Saturn, RPWS observed similar emission in the kHz band as Cassini
flew by Jupiter, and analysis has revealed the presence of striations in that emission.
A statistical study has been performed to investigate the properties of this emission at
Jupiter and Saturn, including its duration, frequency range, drift rate, and source
region location, in order to compare these emissions to observations at Earth.
Jovian
striations are found to emanate from near Io, while the Saturn analog is generated
about 2.2 Saturn radii from the planet.
The results of this study support the findings of
previous research on striations present in Earth's Auroral Kilometric Radiation, which
concluded that these emissions could be explained by the presence of
upward-propagating solitary ion structures.
MOP2011-P0109
Oral (Contributed)
The Hydrogen Atoms in the Saturnian Magnetosphere
Tseng, W. [1], R.E. Johnson [1] and W. Ip [2]
[1] University of Virginia, Materials Science and Engineering
[2] National Central University, Astronomy
The Voyager flyby observation have revealed that, in the Saturnian magnetosphere,
a very broad distribution of the hydrogen atoms existed in a doughnut-shape region
(Broadfoot et al., 1981). Shemansky and Hall (1992) showed that this atomic hydrogen
cloud had an azimuthal asymmetry dependent on local time with higher intensity on
the dusk side. Smyth and Marconi (1993) suggested that the accumulative effect of
solar radiation pressure is important for the long-term orbital motion of the hydrogen
atoms escaping from Titan and would explain this complex 3D morphology. From the
modeling results, Ip (1996) also pointed out that, in addition to the Titan's hydrogen
torus, the sun-lit hemisphere of Saturn's atmosphere and/or the ring system could be
major sources of the hydrogen atoms in the inner magnetosphere.
Recent Cassini
UVIS observations confirm local-time asymmetry but also show the hydrogen cloud
density increases with decreasing distance to Saturn's upper atmosphere (Shemansky
et al., 2009). They suggested that there could be hydrogen plumes flowing outward
from the Saturn's sun-lit hemisphere due to electron-impact dissociation of H2. Since
the neutral hydrogen cloud is an important source of H+ for the magnetosphere, we
initiated a study that expands on our recent description of H2 in Saturn's
magnetosphere (Tseng et al. 2011). In this work, we will study the sources of the atomic
hydrogen cloud: Saturn's atmosphere, the main ring system, the Enceladus' plumes
and the Titan's hydrogen torus. We have found that the ejection velocity and angle
distribution are modified by collisions of the hot hydrogen with the ambient
atmospheric H2 affecting the morphology of Saturn's hydrogen plume. Preliminary
modeling also shows the hydrogen atoms from the dissociation of H2 of the ring
atmosphere could populate ~30% of the total number inside 5 RS observed by UVIS.
The axial asymmetry of Titan's atomic hydrogen torus shaped by the solar radiation
pressure and Saturn's oblateness might account for the observation in the outer
magnetosphere.
MOP2011-P0012
Oral (Contributed)
No Evidence for Erosion of the Saturn Magnetopause by Northward IMF
Lai, H. [1], H.Y. Wei [1], C.T. Russell [1], C.S. Arridge [2] and M.K. Dougherty [3]
[1] University of California, Los Angeles, Institute of Geophysics and Planetary Physics
[2] Mullard, University College London
[3] Astrophysics, ICSTM
We have examined Saturn's magnetopause at local times from 1000 to 1400 for both
evidence of reconnection and evidence that reconnection has a significant effect
on the location of the magnetopause. We first searched for the signatures of flux
transfer events (FTEs) in which flux tubes are formed which connect the
magnetosheath to the magnetosphere and lead to discrete events which transport
magnetic flux to the magnetotail. No such FTEs were found. We then examined the
same subsolar region of the magnetopause for any significant normal components
indicative of even spotty reconnection. Some such significant normal components
were found during portions of some magnetopause crossings. To determine the
significance of any magnetopause erosion that may be associated with this spotty
reconnection, we estimated the radius of the subsolar magnetopause when the
magnetosheath field was southward, and when it was northward. When we did this
for about 80 magnetopause crossings, we found no discernible difference in the
magnetopause location. Hence, reconnection does not appear to play a significant
role in the transport of the magnetic flux from the dayside magnetopause to the
magnetotail at Saturn.
MOP2011-P0013
Oral (Contributed)
The Intrinsic Magnetic Field of Saturn: A Special One or an Averaged One
Cao, H. [1], C.T. Russell [1], U.R. Christensen [2] and M.K. Dougherty [3]
[1] Institute of Geophysics and Planetary Physics, University of California, Los Angeles
[2] Solar System Research, Max Planck Institute
[3] Blackett Laboratory, Imperial College London
The intrinsic magnetic field contains important information about the interior structure
of a planet. The spatial spectrum of the field can be used to estimate the depth of the
dynamo region where the molecular-metallic phase transition occurs. The strength of
the field puts constraints on the available power, and thus thermal budget of the
planet. The secular variation of the field can be used to infer the bulk motion of the
dynamo region and the small scale flows on the dynamo surface, etc.
The Cassini
spacecraft is providing us the first chance to characterize the magnetic field of Saturn
in great detail and to monitor the continuous time evolution of the field. In this study,
we model the contributions to the measured magnetic field from various sources in
the magnetosphere: the ring current, the mysterious ~11h periodic perturbations, the
magnetopause current and tail current, etc. The displacement of the magnetodisk
from the magnetic equator by the oblique incidence of the solar wind is also taken
into account. Modeling the external contributions are conducted on measurements
outside L-shell = 3.8 Rs orbit by orbit. The parameters extracted are then used to
calculate the external field inside L-shell = 3.8 Rs for the corresponding orbit.
After
removing the external contributions orbit by orbit, we search for the non-axisymmetric
components and result in tighter upper bounds. The secular variation rate of the field
is investigated based on yearly grouped observations: no secular variation is found,
the upper limits on the secular variation rate are more constrained. A parameter
search based on the SOI measurements of Cassini which went into 1.3 Rs reveals that
the high degree moments of the field are unexpectedly small and the total field
spectrum shows a zig-zag pattern at the planet surface up to degree 5. More
surprisingly, the spatial spectrum of the odd terms becomes flat at ~0.4 Rs which
implies a much deeper dynamo than previously estimated based on pressure
ionization argument. This deeply seated dynamo is also consistent with the energy flux
scaling laws. The electromagnetic shielding mechanism is also favored to some extent.
This mechanism implies that the Saturn's magnetic field observed is averaged over ~
100,000 years. However, the depression of the even terms points toward another
possibility that the Saturnian dynamo is a special dynamo solution different from the
geodynamo. These possibilities have to be further examined by numerical dynamo
modeling.
MOP2011-P0019
Oral (Contributed)
Saturn's magnetic equinox: results from a survey of the amplitude and
phase of dual-period magnetic field oscillations using Cassini data.
Andrews, D.J.[1], S.W. Cowley [1], M.K. Dougherty [2] and G. Provan [1]
[1] Department of Physics and Astronomy, University of Leicester
[2] Department of Physics, Imperial College
Previous studies have shown the presence of two independently rotating magnetic
perturbation systems at Saturn, intimately connected with Saturn kilometric radiation
(SKR) modulations in the northern and southern hemispheres. During the first ~5 years
of the Cassini mission, the period of the southern system was consistently longer than
the northern, and its field oscillation dominated in the equatorial magnetosphere.
However, it has recently been shown that the periods of the two SKR emissions
converged towards common values some ~9 months after Saturn's vernal equinox in
August 2009, suggesting seasonal control of these phenomena. In view of this new
discovery, we survey the amplitude, phase, and polarisation of the equatorial
magnetic field oscillation for corresponding evidence of secular variation in the
periods and relative field strengths of the two systems. These data provide clear
evidence that the amplitudes of the two systems have become comparable during
the post-equinox epoch, and their implications for the northern and southern
magnetic field periods will also be discussed.
MOP2011-P0021
Oral (Contributed)
The growth of plasma convection in Saturn's inner magnetosphere
LIU, X. [1] and T.W. HILL [1]
[1] RICE UNIVERSITY, ASTRONOMY & PHYSICS
We report Rice Convection Model (RCM) simulations of centrifugally driven plasma
convection in Saturn's inner magnetosphere (2<L<12), incorporating a continuously
active distributed plasma source. The distributed plasma source is a key element that
distinguishes convection at Saturn, where the source is broadly distributed, from that
at Jupiter, where the source is largely confined to the Io torus. At Saturn, the broadly
distributed source produces fast, narrow inflow channels alternating with slower, wider
outflow channels, consistent with Cassini Plasma Spectrometer observations.
Comparison with observed corotation lags indicates that the plasma source model
adopted in earlier RCM simulations needs refinement. We have incorporated newer
plasma source models [Smith et al., 2010, and Cassidy & Johnson, 2010] that imply
much larger plasma mass loading rates and different radial distributions of charge
exchange versus electron impact ionization rates. This modification is partly
compensated by increasing the assumed Pedersen conductance of Saturn's
ionosphere.
MOP2011-P0028
Oral (Contributed)
Influence of negatively charged plume grains on the structure of
Enceladus' Alfven wings: hybrid simulations versus Cassini MAG data
Kriegel, H. [1], S. Simon [2], U. Motschmann [1,3], J. Saur [2], F.M. Neubauer [2], A.
Persoon [4], M.K. Dougherty [5] and D.A. Gurnett [4]
[1] Institute for Theoretical Physics, TU Braunschweig
[2] Institute of Geophysics and Meteorology, University of Cologne
[3] Institute for Planetary Research, German Aerospace Center (DLR)
[4] Department of Physics and Astronomy, University of Iowa
[5] S
We apply the hybrid simulation code A.I.K.E.F. (adaptive ion kinetic electron fluid) to
the interaction between Enceladus' plume and Saturn's magnetospheric plasma. For
the first time, the influence of the electron-absorbing dust grains in the plume on the
plasma structures and magnetic field perturbation, the Alfven wing, is taken into
account within the framework of a global simulation. Our work continues the
analytical calculations by Simon et al., 2011, who showed that electron absorption
within the plume leads to a negative sign of the Hall conductivity. The resulting twist
of the magnetic field, referred to as the Anti-Hall effect, has been
all targeted Enceladus flybys between 2005 and 2010.
observed during
We show that <br> (1)
applying a plume model that considers both, the neutral gas and the dust allows us to
quantitatively explain Cassini Magnetometer (MAG) data,<br> (2) dust enhances the
anti-Saturnward deflection of the ions, causing asymmetries which are evident in the
MAG data,<br> (3) the ions in the plume are slowed down below 1 km/s.<br> (4)
Besides, we compare our results to MAG data in order to systematically analyze
variations in the plume activity and orientation
(E5,E6), (E7,E9) and (E8,E11).
for selected pairs of similar flybys:
MOP2011-P0036
Oral (Contributed)
Mapping Jupiter's auroral features to magnetospheric sources:
Comparing results from three different models for Jupiter's ionospheric
magnetic field
Vogt, M.F.[1,2], M.G. Kivelson [1,2,3], K.K. Khurana [1], R.J. Walker [1,2], B. Bonfond [4],
D. Grodent [4] and A. Radioti [4]
[1] Institute of Geophysics and Planetary Physics, UCLA
[2] Department of Earth and Space Sciences, UCLA
[3] Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan
[4] LPAP, Institut d'Astrophysique et de G?ophysique, Universit? de
Despite the advances made from over a decade of Hubble Space Telescope (HST)
observations and complementary theoretical studies, many fundamental questions
regarding the nature and causes of Jupiter's auroral emissions have remained
unanswered. Part of the difficulty results from the lack of accurate, global Jovian field
models that can be reliably used for mapping beyond ~30 R J. In a recent study [Vogt
et al., 2011] we employed a flux equivalence approach to provide a reliable,
data-based magnetospheric mapping of Jupiter's polar auroral emissions to the
middle and outer magnetosphere. We concluded that the polar auroral active
region can be interpreted as Jupiter's polar cusp and that the swirl region can be
interpreted as Jupiter's polar cap. Additionally, we calculated that the area of
Jupiter's polar cap is equivalent to a circle around the pole with an ~11? radius
(slightly smaller than ~15? for the terrestrial polar cap) and the open flux through that
region is ~720 GWb. The flux equivalence calculation used in our study required
knowledge of the northern ionospheric magnetic field, for which we used the model
of Grodent et al. [2008] because it accurately matches the ionospheric positions of
the satellite footprints in the northern hemisphere to their orbital distances in the
magnetosphere. However, other internal field models are available, each with its
advantages and limitation, including VIP4 [Connerney et al., 1998] and the "VIPAL"
model, based on recent work by Hess et al. [2011]. In this study we will compare the
previously published mapping results with the Grodent et al. [2008] model to new
results that used the VIP4 and VIPAL models in the flux calculation, placing particular
emphasis on any differences in the resulting polar cap size and location or the
amount of open flux. We will also discuss how the polar cap location shifts its
jovigraphic location over a rotation period.
MOP2011-P0048
Variations of 3-220
Magnetosphere
Oral (Contributed)
keV/e
Ions
with
Energy
and
L
in
Saturn's
DiFabio, R. [1], D. Hamilton [1], T. Krimigis [2,3] and D. Mitchell [2]
[1] Physics, University of Maryland
[2] Applied Physics Laboratory, Johns Hopkins University
[3] Office for Space Research and Technology, Academy of Athens
Studying the ion composition of Saturn's magnetosphere provides insight into the
strength of the different plasma sources. We use the Charge-Energy-Mass
Spectrometer (CHEMS) on Cassini to study energy and L variations of the suprathermal
(E/Q=3-220 keV/e) ion composition in Saturn's magnetosphere. We combine the data
from 78 equatorial (Latitude=-10 degrees to 10 degrees) passes from 2004-2010 and
calculate the partial number density in delta L=1 bins from L=6-21. The species
examined are H+, W+, H2+, He++, He+, and O++. These species are tracers for various
plasma sources: W+ and O++ from Enceladus, H+ (mixed Saturn, Enceladus, and solar
wind), H2+ from Titan, and He++ and He+ from the solar wind and interplanetary
pick-up ions. <br><br>The number density of suprathermal ions increases inward to
about L~9-10 and then drops due to collisions with Saturn's neutral cloud. W+ and H+
dominate the number density, and the H+/W+ ratio tends to increase with energy.
H2+ is the third most abundant species, except in Saturn's inner magnetosphere (L < 7)
where loss processes result in the H2+ number density dropping below the O++ density.
The largest source of O++ is electron impact ionization of O+, which originates largely
from Enceladus, but the ionization of > 150 keV O+ via collisions with Saturn's neutral
cloud is a significant source for energetic O++. He+ and He++ are the least abundant
species and their fractional abundances decrease inward for all energies.
MOP2011-P0064
Oral (Contributed)
Variations of the auroral emission from Io's atmosphere
Roth, L. [1], J. Saur [1], P. Feldman [3], D. Strobel [2] and K. Retherford [4]
[1] University of Cologne, Institute of Geophysics
[2] Department of Earth and Planetary Sciences, Johns Hopkins University
[3] Department of Physics and Astronomy, Johns Hopkins University
[4] Department of Space Science, Southwest Research Institute
We analyze a set of observations of Io's auroral emission in order to find characteristics
of
its temporal variations. The auroral radiation is generated in Io's atmosphere by
collisions between impinging magnetospheric electrons and the neutral gas particles.
Spatially resolved OI1356 ? emission is extracted from 38 observations of Io's dayside
atmosphere taken by the Space Telescope Imaging Spectrograph (STIS) onboard the
Hubble Space Telescope (HST) between 1997 and 2001.
We construct a
phenomenological model that describes the three dimensional distribution of the
auroral emission in Io's vicinity to reproduce the observed morphologies. Assuming
that the emission distribution depends only on the properties of the surrounding
plasma, we generate model images by integrating along the respective line-of-sight
over the local emission taking into account the plasma environment of each
exposure. The model parameters are then fitted to match all 38 observations with one
parameter set.
We finally look for minor variations on the dayside atmosphere and
changes during eclipse to infer possible variations of Io's atmosphere.
MOP2011-P0065
Oral (Contributed)
Callisto's Plasma Interaction and Induced Fields from a Subsurface
Ocean
Seufert, M. [1], J. Saur [1] and F.M. Neubauer [1]
[1] University of Cologne, Institute of Geophysics and Meteorology
We present a MHD-model for the sub-Alfv?nic interaction of Callisto with the
surrounding magnetospheric plasma and a model for the magnetic fields induced in
a possible subsurface liquid water ocean and compare the results to magnetometer
data for several flybys of the Galileo spacecraft. The existence of a subsurface ocean
was proposed e.g. by Kivelson et al. 1999 and Zimmer et al. 2000 based on
magnetometer data analysis. However, none of these previous studies included
detailed modeling of Callisto's plasma interaction. For the first time we present
MHD-models for the plasma interaction for several flybys of Galileo at Callisto. Based
on a model for Callisto's plasma environment for these flybys we conduct 3D-MHD
simulations of the interaction of the plasma with the satellites atmosphere and
ionosphere. We further present a model for the magnetic fields induced in the interior
based on a realistic multi-layer conductivity structure including a subsurface ocean.
The magnetic signatures predicted by the plasma interaction model and the
induction model are then compared with Galileo magnetometer data. The final goal
of this study is to deduce information for the configuration of Callisto's ocean layer
and atmosphere from the magnetic field data.
MOP2011-P0090
Oral (Contributed)
Density trends of negative ions at Titan
Wellbrock, A. [1], A.J. Coates [1], G.H. Jones [1], C.S. Arridge [1], G.R. Lewis [1], D.T.
Young [2], J.H. Waite [2], F.J. Crary [2] and E.C. Sittler [3]
[1] Mullard Space Science Laboratory, Univeristy College London
[2] Space Science and Engineering Division, Southwest Research Institute
[3] Goddard Space Flight Center, NASA
The Electron Spectrometer part of the Cassini Plasma Spectrometer (CAPS-ELS) has
revealed the existence of negative ions in Titan's ionosphere (Coates et al, 2007,
Waite et al, 2007). These are observed during every encounter when the instrument
points in the ram direction at altitudes between 950 and 1400 km. The heaviest ions
observed so far have masses up to 13 800 amu/q. This indicates that complex
hydrocarbon and nitrile chemical processes take place in Titan's upper atmosphere,
probably playing a role in haze formation. Even heavier particles such as tholins can
form which fall to lower altitudes and build up on Titan's surface (Coates et al, 2009).
With data from over 25 encounters and taking advantage of an increase in the duty
cycle of measurements during recent flybys we have accumulated a large negative
ion database. Coates et al. (2009) discussed trends in the highest masses observed
with solar zenith angle (SZA), altitude and latitude. We are extending this study to
density trends of different masses. Groups of masses can be identified because
recurrent peaks are observed in the 'mass' spectra of different encounters. We
investigate the effects of different controlling parameters such as altitude, solar zenith
angle, latitude, Titan local time, and the angle between magnetospheric co-rotation
and solar ionisation sources. The aim of this study is to help constrain the chemical
formation and destruction processes of negative ions in Titan's ionosphere. We present
the results and discuss their implications. For instance, for higher masses of 110-200
amu at an altitude range of 950 - 1050 km the highest densities are found on the
nightside, whereas the highest densities of low masses (10 - 30 amu) are found on the
dayside at low SZAs in the same altitude range. Therefore, nightside reactions seem to
yield the highest densities for higher masses and photochemical reactions yield the
highest densities for the lower mass negative ions. We also investigate the
microchannel plate efficiency that is used to calculate the negative ions densities.
MOP2011-P0094
Oral (Contributed)
Influence of Upstream Solar Wind on Thermospheric Flows at Jupiter
Yates, J.N.[1,2], N. Achilleos [1,2] and P. Guio [1,2]
[1] Department of Physics and Astronomy, University College London
[2] Centre for Planetary Sciences at UCL/Birkbeck, University College London
Jupiter's
auroral
emissions
are
an
important
observational
signature
of
magnetosphere-ionosphere coupling. Using the 2D UCL Jovian code, we have
simulated how varying dynamic pressure in the upstream solar wind affects
magnetosphere-ionosphere coupling currents, and the ensuing momentum balance
of atmospheric flows. Three different magnetic field profiles representing compressed,
averaged and expanded `middle' magnetospheres were calculated to represent
differing solar wind conditions. These profiles, coupled to an azimuthally symmetric
global circulation model, were then used to solve for the magnetosphere's plasma
angular velocity. The magnetosphere-ionosphere coupling currents determined using
the plasma angular velocity affect thermospheric flows, momentum balance and
energy input. We find that advection and ion drag play an important role in
balancing momentum in the lower altitudes of the thermosphere (near the auroral
ionization peak). The power dissipated within the thermosphere by Joule heating and
ion drag respectively increases by 190 % and 185 % between our compressed and
expanded models.
MOP2011-P0001
Either (Contributed)
Cassini observations of ion and electron beams and their relationship to
infrared auroral arcs
Badman, S.V. [1], N. Achilleos [2], C.S. Arridge [3], K.H. Baines [4], R.H. Brown [5], E.J.
Bunce [6], A.J. Coates [3], S.W.H. Cowley [6], M.K. Dougherty [7], M. Fujimoto [1], G.
Hospodarsky [8], S. Kasahara [1], T. Kimura [1], H. Melin [6], D.G. Mitchell [9], T.
Stallard [6], and C. Tao [1]
[1] JAXA ISAS, Sagamihara, Japan
[2] Atmospheric Physics Lab, UCL, London, UK
[3] MSSL, UCL, London, UK
[4] SSEC, University of Wisconsin-Madison, Madison, USA
[5] LPL, University of Arizona, Tucson, USA
[6] Dept of Physics and Astronomy, University of Leicester, Leicester, UK
[7] Space and Atmospheric Physics, Imperial College London, London, UK
[8] Radio and Plasma Wave Group, University of Iowa, Iowa, USA
[9] APL, Johns Hopkins University, Laurel, USA
We present VIMS images of infrared auroral emissions from the northern noon ionosphere sector
revealing multiple intense auroral arcs poleward of the main oval. At the Earth, such auroral arcs
are signatures of transient magnetopause reconnection events (Milan et al., 2000).
Simultaneous
MIMI/INCA observations show field-aligned H ion bursts travelling upward from Saturn's ionosphere.
These pulsed ion conics were accompanied by energetic electron beams (MIMI/LEMMS, ELS),
electrostatic and electromagnetic wave signatures (RPWS) and evidence of layered field-aligned
current structures moving over the spacecraft (MAG).
We propose that the ion beams are
accelerated out of the ionosphere in downward current regions via wave-particle interactions
(Carlson et al., 1998; Mitchell et al., 2009) and the bright auroral arcs result from electron
precipitation on the adjacent layered upward current regions.
Reference
Carlson, C.W. et al., GRL, doi: 10.1029/98GL00851, 1998.
Milan, S.E. et al., JGR, 105, 2000.
Mitchell, D.G. et al., JGR, doi: 10.1029/2008JA013621, 2009.
MOP2011-P0018
Either (Contributed)
Dual periodicities in 'planetary period' magnetic field oscillations in
Saturn's tail
Provan, G. [1], D.J. Andrews [1], A.J. Coates [2], S.W. Cowley [1], G. Cox [1], M.K.
Doughety [3] and C.M. Jackman [4]
[1] Physics and Astronomy, University of Leicester
[2] Mullard Space Science Laboaratory, University College London
[3] Blackett Laboratory, Imperial College London
[4] Physics and Astronomy, University College London
Planetary period oscillations in Saturn's plasma sheet exhibit dual periodicities,
oscillating predominantly at the Northern Saturn Kilometric Radiation (SKR) period
(Lamy, 2011) at heights greater than 3 Rs (1 RS = 60268 km) above the modelled
current sheet (Arridge et al., 2006) and at the Southern SKR period (Lamy, 2011) below
this.
For both the Northern and the Southern systems the plasma sheet has a
maximum upward displacement when the radial component of the quasi-uniform
'core' field (Andrews et al, 2008, Provan et al., 2011) is pointing outwards, and a
maximum downward displacement when the radial component of the quasi-uniform
field is pointing inwards These results are derived from examining oscillations during
ten orbital revolutions (Revs) during 2006, when Cassini performed a sequence of flank
and tail orbits passing through the plasma sheet region to maximum distances of ~60
Rs and beyond.
The earliest Revs are located near the planet's equatorial plane,
whilst on the later Revs Cassini passes into the northern hemisphere. In the equatorial
region Cassini is located on southern hemisphere magnetic field lines due to the
south-to-north flow of the solar wind during the interval studied [Cowley et al., 2006,
Arridge et al., 2008].
Two new phase models are derived describing the
planetary-period oscillations at Southern and Northern (SKR) corrected for radial and
azimuthal propagation of the phase fronts valid to a radial distance of 60 Rs.
MOP2011-P0034
Either (Contributed)
Field-Aligned Currents Associated with Interchange Injection at Saturn
DeJong, A. [1], R. Livi [1] and J. Burch [1]
[1] Southwest Research Institute, Space Science and Engineering Division
Centrifugal interchange instability at Saturn causes magnetic flux tubes containing
low density, high temperature plasma to replace dense, cold plasma in Saturn's inner
magnetosphere.
DeJong et al. [2010] found that electrons in the 10-100 eV range
are associated with interchange injections.
When separated by pitch
angle, the
field-aligned electrons in this energy range have an enhanced flux relative to the
trapped electrons.
This indicates that the field-aligned currents associated with the
interchange injections may be carried by the cooler, 10-100 eV electrons.
We
present the initial results from an investigation of these field-aligned currents
associated with interchange injections associated with enhanced fluxes in the 10-100
eV electrons.
MOP2011-P0052
Either (Contributed)
Multi-fluid MHD study on Ion Loss from Titan's Atmosphere
Ma, Y. [1], C.T. Russell [1], A.F. Nagy [2], G. Toth [2], M.K. Doughty [3] and T.E.
Cravens [4]
[1] IGPP, UCLA
[2] Department of Atmospheric, Oceanic and Space Sciences, University of Michigan
[3] Space and Atmospheric Physics Group, Imperial College London
[4] Department of Physics and Astronomy, University of Kansas
We study the plasma interaction around Titan using a newly developed three
dimensional multi-fluid MHD model similar to the one that has been recently applied
to Mars [Najib et al., 2011]. The multi-fluid MHD model of Titan solves separate
continuity, momentum, and pressure equations for seven ion species which are
important in either Titan's ionosphere or in the ambient plasma. The code uses a
spherical grid structure with high radial resolution ~ 30 km in the lower ionosphere. We
apply the model to an idealized case of Titan and compare in detail with the single
fluid model using the same set of plasma parameters to illustrate the importance of
multi-fluid effects near Titan.
MOP2011-P0054
Either (Contributed)
Kelvin-Helmholtz Instability at Saturn's Magnetopause: Cassini Ion Data
Analysis and Hybrid Simulation
Delamere, P. [1], R.J. Wilson [1] and F. Bagenal [1]
[1] University of Colorado, Laboratory for Atmospheric and Space Physics
On December 13, 2004, the Cassini spacecraft, on approach to Saturn from near the
dawn flank, crossed the magnetopause multiple times.
During these boundary
crossings the Cassini Plasma Spectrometer (CAPS) had a good view of both the
magnetospheric and the magnetosheath plasmas.
We derive, for the first time,
CAPS plasma properties (ion temperature, density, composition, and plasma flow)
during these magnetopause boundary encounters. Previous work by Masters et al.
[2009], utilizing magnetometer and thermal electron data, identified within this region
a Kelvin-Helmholtz vortex.
Kelvin-Helmholtz vortices can mediate the transport of
mass, momentum, energy and magnetic flux at the magnetospheric boundaries,
making KHI an important mechanism through which the solar wind interacts with the
magnetosphere.
We use our derived plasma properties as input parameters for a
two-dimensional hybrid simulation of the KHI unstable magnetopause boundary. We
investigate the effect of heavy magnetospheric ions on the KHI evolution and test the
growth rates as a function of magnetosonic Mach number. We compare our
simulation results with the plasma data, estimate diffusion coefficients due to KHI
plasma mixing (D > 1010 m2 s-1) and energy transported into Saturn's magnetosphere (~
40 GW) due to the KHI unstable boundaries and conclude that mass transfer
processes at Saturn's magnetospheric boundaries can play a significant role in driving
magnetospheric dynamics.
MOP2011-P0058
Either (Contributed)
Investigation of the low latitude outer magnetosphere of Saturn using ion
data measured by the Cassini Plasma Spectrometer
Szego, K. [1], Z. Nemeth [1], G. Erdos [1], L. Fioldy [1], M. Thomsen [2] and D. Delapp
[2]
[1] KFKI Research Institute for Particle and Nuclear Physics, Space Physics
[2] Los Alamos National Laboratory, National Laboratory
We investigated the low latitude (-10deg < lat < 10deg ) outer magnetosphere (10 R_S
< R < 22 R_S) of Saturn using ion data measured by the Cassini Plasma Spectrometer
onboard Cassini during the prime mission. The objectives were a) to characterize
systematically and quantitatively the upstream ion density of thermal ions for the Titan
encounters of Cassini during the prime mission; b) the characterization of the
magnetodisk in the low latitude outer magnetosphere, near Titan's orbit. These two
objectives are intimately correlated. We used two different approaches. First, using
dynamic energy spectra of ions we showed that 12h long intervals around the Titan
encounters generally include plasma sheet and lobe type regions, and a special one,
a short event, rich in heavy ions. Detailed study of these events revealed the fine
structure of the magnetodisk of Saturn, having a narrow central sheet of very high
heavy ion content, heavy rich events occurring when the spacecraft crosses this
central sheet. We also proved that the heavy rich events appear periodically in
longitude, but with a period slightly (by 0.35deg /day) longer than the SLS3 period. The
second approach is based on ion moments derived at Los Alamos National
Laboratory. Along Titan flyby orbits the plasma sheet is denser and wider on the
dayside of Saturn than on the nightside; in the lobes the protons were dominant. A
peculiar feature of the heavy ion density values in the sheet is that they are spiky and
do not exhibit smooth variation; this has not been identified before. At these locations
the heavy ion density is the highest. This correlates well with the heavy rich events
found by the dynamic spectra. The central line of the magnetodisk is surrounded by a
structured plasma sheet, a smooth, broad ion layer composed of light ions, and a
heavy ion layer displaying narrow substructures. High heavy ion density in the sheet is
accompanied by low heavy ion temperature. The proton density shows periodic
modulation due to the flapping of the magnetodisk relative to the spacecraft, similar
to those found for thermal electrons by Arridge et al. The ion plasma density shows
periodical fluctuations in the distant regions, with similar periodicity observed in the
magnetic field data. The upstream plasma environment of Titan is basically defined
by its distance from the magnetic equator, globally this correlates with the SLS3
longitude of Titan during encounters.
MOP2011-P0061
Either (Contributed)
Longitudinal modulation of hot electrons in the Io plasma torus.
Hess, S. [1,2], P.A. Delamere [2], F. Bagenal [2], N.M. Schneider [2] and A.J. Steffl [3]
[1] LATMOS, Universit? Versailles St Quentin - CNRS
[2] LASP, University of Colorado
[3] SwRI, SwRI
The longitudinal modulation in the Io torus has been an open question for decades. A
major clue was provided by the discovery of the key modulation of the hot electron
population, at both the System III and System IV periods. However, very little progress
has been made in explaining the origin of these hot electron modulations. We
propose that the hot electrons population is powered by the inward motion of empty
flux tubes (i.e. related to the outward transport of the Iogenic plasma), which has
been observed in the torus. We propose that the System IV and System III modulation
of the hot electron population corresponds to modulation of the intensity of the
current system and of the efficiency of the electron acceleration, respectively. We
build on the latest models of the Io current system to describe the current system
associated with the motion of the empty flux tubes, and the associated electron
acceleration. The System III modulation of the hot electron population, due to the
modulation of the efficiency of the electron acceleration, can then be related to the
topology of the magnetic field. We show through calculation and simulation that the
electron acceleration related to the inward motion of the empty flux tube may
explain the observations. We discuss the energy budget and show that it is in favor of
our hypothesis.
MOP2011-P0079
Either (Contributed)
Magnetotail reconnection and flux circulation: Jupiter and Saturn
compared
Jackman, C.M.[1], M.F. Vogt [2], J.A. Slavin [3], S.W. Cowley [4] and S.A. Boardsen
[5]
[1] Department of Physics and Astronomy, University College London
[2] Department of Earth and Space Sciences, UCLA
[3] Heliophysics Science Division, NASA Goddard Space Flight Center
[4] Department of Physics and Astronomy, University of Leicester
[5] Go
The Jovian magnetosphere has been visited by eight spacecraft, and the
magnetometer data have been used to identify dozens of plasmoids and ~250 field
dipolarizations associated with magnetic reconnection in the tail [e.g. Vogt et al.,
2010].
Since the arrival of the Cassini spacecraft at Saturn in 2004, the
magnetometer instrument has also been used to identify reconnection signatures.
The deepest magnetotail orbits were in 2006, and during this time 34 signatures of
plasmoids were identified. In this study we compare the statistical properties of
plasmoids at Jupiter and Saturn such as duration, size, location, and recurrence
period.
Such parameters can be influenced by many factors, including the different
Dungey cycle timescales and cross-magnetospheric potential drops at the two
planets. We present superposed epoch analyses of plasmoids at the two planets to
determine their average properties and to infer their role in the reconfiguration of the
nightside of the magnetosphere.
We examine the contributions of plasmoids to the
magnetic flux transfer cycle at both planets. At Jupiter, there is evidence of an
extended interval after reconnection where the field remains northward (analogous
to the terrestrial post-plasmoid plasma sheet). At Saturn we see a similar feature, and
calculate the amount of flux closed on average in reconnection events, leading us to
an estimation of the recurrence rate of plasmoid release.
MOP2011-P0103
Either (Contributed)
Cassini INMS Measurements of Ions and Neutrals in Saturn's Inner
Magnetosphere
Perry, M.E.[1], T.E. Cravens [2], K. Mandt [3], B. Teolis [3], H.T. Smith [1], R.L. McNutt, Jr.
[1], J.H. Waite [3] and R. Tokar [4]
[1] JHU/APL, Space Department
[2] Department of Physics and Astronomy, University of Kansas
[3] Space, Southwest Research Institute
[4] Space, Los Alamos National Laboratory
Several times over the past four years, the Cassini Ion Neutral Mass Spectrometer
(INMS) observed neutral molecules, water-group ions, or both in Saturn's inner
magnetosphere near the equatorial plane. These measurements span the region
between 4 and 6 Saturn radii (RS). Although the coverage is sparse, we show that the
vertical, radial, and azimuthal distribution of the observed neutrals is compatible with
models of the neutral cloud that disperses from its source, the plumes of Enceladus.
The INMS detection limit for neutral water density is about
10 3 molecules/cm3, which
INMS observes at several locations in the neutral cloud. Just north of Enceladus, in the
densest part of the neutral cloud outside the plumes, INMS measures
10 3
molecules/cm3. For ions, INMS measures only a small portion of velocity phase space,
but INMS can unambiguously determine the distribution within the water group. INMS
ion observations are consistent with Cassini Plasma Spectrometer data on the
combined water group ions. The INMS observations of water-group ion distributions
agree with models that show that the water-group distribution is comprised almost
entirely of H2O+ near 4 RS and transitions to a region beyond 5.5 RS that is poor in H2O+.
MOP2011-P0104
Either (Contributed)
The Michigan Solar WInd Model (mSWiM) Extended With STEREO A and B
Data: Results and Validation
Hansen, K. [1]
[1] University of Michigan, AOSS
The Michigan Solar WInd Model (mSWiM) has been used extensively to study the
propagation of the solar wind radially outward in the solar system and as a tool for
correlative studies at outer planet magnetospheres. A detailed validation showed
that the method works very well during a period centered on apparent opposition of
±30 days and reasonably well out to ±75 days with mean statistical accuracies as high
as ±15 hours.
Using the OMNI data, derived from Earth based satellites, the method
can provide solar wind conditions at any given target for only 2-4 months per year.
However, the recent availability of STEREO data now allows us to extend this range.
Currently STEREO A and B are each ~90° separated from the Earth and are continuing
to seperate.
Three propagations, one each from the Earth and STEREO A and
STEREO B could yield solar wind predictions that cover as much as 6-12 months of the
year.
We will present results from our propagations of the STEREO A and B data out to
Saturn and show the availability of the propagations, some interesting events and
some additional validation.
Because the spacecraft started their solar orbits near the
Earth and spent a significant amount of time close together, the possibility exists to
perform cross calibrations of the three propagations over a several year time span.
We will present results from these cross calibrations.
(http://mswim.engin.umich.edu)
MOP2011-P0120
Either (Contributed)
Surface charging of Saturn's moon Rhea
Jones, G.H.[1,2], E. Roussos [3], A.J. Coates [1,2] and F. Crary [4]
[1] Mullard Space Science Laboratory, University College London
[2] Centre for Planetary Sciences at UCL/Birkbeck, University College London
[3] Max Planck Institut fuer Sonnensystemforschung, Max-Planck-Str. 2
[4] Southwest Research Institute, San Antoni
Saturn's second-largest moon, Rhea, resides within the planet's magnetosphere, and is
continuously exposed to the magnetospheric plasma population. We report on
Cassini Plasma Spectrometer (CAPS) observations made during the Cassini
spacecraft's close encounters with Rhea on March 2, 2010, and January 11, 2011;
these demonstrate the fascinating physical processes that occur near solid body
surfaces. During the flybys, Cassini passed a few tens of kilometres of the north and
south polar regions of the satellite, respectively. The CAPS Electron Spectrometer, ELS,
had good pitch angle coverage during the encounters, with its 8 anodes covering
directions from towards, to away from the moon. CAPS-ELS observed the expected
decrease in the high energy electron population caused by their absorption by Rhea,
but also observed an enhancement in the population of electrons at energies below
a few hundred eV. We present our interpretation of this population as being
associated wi! th the surface charging of Rhea. At the time of both encounters, the
moon's surface was negatively charged, meaning it could reflect certain incoming
electrons before they struck the ground, and could also accelerate low energy
electrons liberated near the surface. Implications of the observations are discussed.
MOP2011-P0122
Either (Contributed)
Plasma IMS Composition Measurements for Europa, Ganymede, and the
Jovian System
Sittler, E.C.[1], J.F. Cooper [1], R.E. Hartle [1], W.R. Paterson [1], E.R. Christian [1], A.S.
Lipatov [2], P.R. Mahaffy [1], N. Paschalidis [1], M. Sarantos [2], M.A. Coplan [3], T.A.
Cassidy [4] and P. Wurz [5]
[1] NASA Goddard Space Flight Center, Heliophysics Laboratory
[2] GPHI, University of Maryland Baltimore County
[3] Institute for Physics Science and Technology, University of Maryland
[4] Planetary Science, Jet Propulsion Laboratory
[5] Physikalisches In
NASA and ESA are now planning a reduced version of the joint Europa Jupiter System
Mission (EJSM), potentially including a radically descoped Jupiter Europa Orbiter (JEO)
but still with magnetometer and plasma instruments. Similar field and plasma
instrumentation would also reside on ESA Jupiter Ganymede Orbiter (JGO), which
conceivably could carry out multiple flybys of Europa before entering orbit at
Ganymede. We are developing the 3D Ion Mass Spectrometer (IMS) designed to
measure both major and minor ion species within the high radiation environment of
Jupiter magnetosphere and the icy Galilean moons. The IMS covers the energy range
from 10 eV to 30 keV, wide field-of-view (FOV) capability and 10 to 60 sec time
resolution for major ions. This instrument has two main goals: 1) measure the plasma
interaction between Europa and Jupiter magnetosphere and 2) infer the global
surface composition to trace elemental and significant isotopic levels; these goals are
also applicable for in situ measurements at Ganymede and Callisto, and remotely
everywhere via the iogenic plasma for Io. The first goal supports the magnetometer
(MAG) measurements, primarily directed at detection of Europa sub-surface ocean,
while the second goal gives information about transfer of material between the
Galilean moons, e.g. mainly from Io to the other moons, and further allows detection
of oceanic materials emergent to the moon surfaces from subsurface layers
putatively including salt water oceans.
Outgassed exospheric materials are probed
by the IMS by measuring pickup ions accelerated up to spacecraft altitudes of
100
to 200 km in electric fields extending through the local magnetospheric environment
and moon exosphere to the surface. Our 3D hybrid kinetic model of the moon
magnetosphere interaction is used to construct a global model of electric and
magnetic fields for tracing of pickup ion trajectories back to the sources at
approximate surface resolution of 100 km. We show that Europa exospheric
ionosphere is dominated by pickup ions with energies of 100 to 1000 eV. We also
expect field aligned polar ion outflows driven by ionospheric electrons via the
polarization electric field at Europa; the IMS will observe such outflows and thus
sample the ionosphere below spacecraft orbit altitude 100 km. Based on previous
Ganymede studies, we also comment on IMS applications to a Ganymede orbiter.
The IMS and the Europa interaction model are respectively being developed with
support from NASA Astrobiology Instrument Development (ASTID) and Outer Planets
Research (OPR) programs.
MOP2011-P0125
Either (Contributed)
Energetic Electrons in the Jovian Magnetosphere Detected by the Alice
UV Spectrograph Aboard New Horizons
Steffl, A.J.[1], A.B. Shinn [1], M.J. Desroche [2], G.R. Gladstone [3], J.W. Parker [1], K.D.
Retherford [3], D.C. Slater [3], M.H. Versteeg [3] and S.A. Stern [4]
[1] Department of Space Studies, Southwest Research Institute
[2] Laboratory for Atmospheric and Space Physics, Univeristy of Colorado
[3] Space Science and Engineering Division, Southwest Research Institute
[4] Space Science and Engineering Division, Sou
In addition to SWAP and PEPSSI, the two instruments dedicated to measuring in situ
particle fluxes, the New Horizons spacecraft is equipped with a third instrument that is
sensitive to high energy electrons: the Alice UV spectrograph. Electrons with energy >
470 keV can penetrate the thin aluminum housing of Alice and interact with the
microchannel plate detector, producing a count that is indistinguishable from a
photon event. When both instruments are operating, the count rates of Alice and the
Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) electron sensors
are highly correlated, confirming that the Alice count rate serves as a direct measure
of the energetic electron flux at New Horizons, especially during times when the Alice
aperture door was closed and no FUV photons could reach the detector. Over a
10-day period beginning on 22 February 2007, Alice recorded the integrated detector
count rate with a duty cycle of 44%. Since the Alice count rate was sampled once per
second, this data has the highest time resolution of any data set of energetic electron
fluxes at Jupiter, although it is lacking any spatial or energy resolution. Alice observed
an upstream solar wind event while 110 R J from Jupiter. One and a half days later,
Alice observed the magnetopause crossing at a distance of 67~R J, suggesting the
Jovian magnetosphere was in a compressed state during the New Horizons
encounter. During the inbound leg of Jupiter flyby, Alice observed the energetic
electron flux to be intense and highly variable. After closest approach, data from
Alice and PEPSSI show spikes in count rate every five hours, the signature of the Jovian
current sheet crossing over the spacecraft. During periods when New Horizons was out
of the current sheet, the Alice count rate dropped to within a factor of two of the
pre-Jupiter background levels, suggesting that the energetic electrons on these flux
tubes have been lost.
MOP2011-P0029
Either (Contributed)
Current - Voltage Relationships in the Saturnian System
Ray, L.C.[1], M. Galand [1], B. Fleshman [2] and R.E. Ergun [3]
[1] Space and Atmospheric Physics Group /, Imperial College
[2] Department of Physics, University of Oklahoma
[3] Laboratory for Atmospheric and Space Physics / Dept. of Astrophysical and Planetary Science,
University of Colorado
Saturn's magnetosphere and ionosphere are coupled by field-aligned currents that
transfer angular momentum between the two regions. The heavy magnetospheric
water group ions are centrifugally confined to the equatorial plane due to Saturn's
rapid rotation rate.
As a consequence, an ambipolar electric field develops along
the magnetic field lines to maintain quasi-neutrality along the flux tube.
This restricts
the mobility of the current-carrying electrons. If the magnetospheric demand for
angular momentum exceeds that which can be transferred by the thermal electrons,
field-aligned potentials will develop at high-latitudes, between 1 and 2 Saturnian radii,
to increase current flow. We use a 1-D spatial 2-D velocity space Vlasov code to
model the current-voltage relationships in the Saturnian system for flux tubes mapping
to 4 RS near Enceladus's orbit and to 9 RS in the middle magnetosphere where faint
aurora has been detected in the UV.
We show that the current - voltage relationship
is dictated by the location of the acceleration region and the plasma population at
high-latitudes.
Additionally, we calculate the incident electron energy fluxes at the
ionosphere and compare our values with those inferred from the analysis of auroral
emissions.
MOP2011-P0049
Either (Contributed)
The Interaction Between the Solar Wind and Jupiter's Magnetosphere
Desroche, M. [1,3], F. Bagenal [2,3], P. Delamere [3], N. Erkaev [6], C. Farrugia [4]
and H. Biernat [5]
[1] Department of Physics, University of Colorado Boulder
[2] Department of Astrophysical and Planetary Sciences, University of Colorado Boulder
[3] Laboratory for Atmospheric and Space Physics, University of Colorado Boulder
[4] Institute for the Study o
We have developed a method of exploring properties on either side of Jupiter's
magnetopause that allows us to evaluate the transfer of mass and momentum across
the boundary.
We are treating the magnetopause as a tangential discontinuity,
the shape of which is given by a nonaxisymmetric paraboloid,based on theoretical
modeling (Engle and Beard, JGR 85, 1980;
(Slavin et al, JGR 90, 1985).
Stahara et al, JGR 94, 1989) and data
We compare the plasma flows, densities, and magnetic
fields on either side of the magnetopause boundary to determine regions along the
magnetopause that are susceptible to the Kelvin-Helmholtz instability (KHI).
We also
consider the possibility of large-scale reconnection based on the magnetic field shear
angle and magnitude. <br>
The Khurana magnetic field model, which includes a
plasma sheet, radial currents, and magnetopause currents (Khurana and Schwarzl,
JGR 110, 2005), provides the magnetic field information in the magnetosphere.
A
simple model based on Galileo measurements is used to describe the plasma flows
and density in the magnetosphere.
In the magnetosheath we are using results
obtained by the numerical integration of the dissipationless MHD equations (Erkaev et
al, JGR 101, 1996; Farrugia et al, Planet. Space. Sci. 46, 1998) for the case of solar wind
flow past a nonaxisymmetric tangential discontinuity.
Due to the flattened shape of
the magnetopause, flow is increased towards the poles. This results in a rotation of
the IMF towards the direction of the planet's rotational axis. <br>
With these
models we test the onset criterion for the KHI, and find that, due to the large shear
flows and rotation of the magnetic field in the magnetosheath, both flanks exhibit
regions susceptible to the instability.
We find also that the magnetic fields approach
an antiparallel configuration in some regions, though the shear magnitude is generally
weaker than the reconnection onset criterion considered at Earth (e.g. by Cooling et
al, JGR 106, 2001).
MOP2011-P0074
Either (Contributed)
Simultaneous multi-wavelength observations of Saturn's aurorae : energy
budget and magnetospheric dynamics
Lamy, L. [1], R. Prang? [1], J. Gustin [2], W. Pryor [3], B. Cecconi [1], P. Zarka [1], S.
Badman [4], T. Stallard [5], D. Mitchell [6] and P. Brandt [6]
[1] Observatory of Paris, LESIA
[2] Universit? de Li?ge, LPAP
[3] Central Arizona College, Astronomy and Geology
[4] JAXA, Institute of Space and Astronautical science
[5] University of Leicester, Department of Physics and Astronomy
[6] John Hopkins Unive
Similarly to other magnetized planets, accelerated electrons entering Saturn's auroral
regions generate powerful emissions. They divide into Ultraviolet (UV) and Infrared (IR)
aurorae, originating from collisions with the upper atmosphere, and Saturn's Kilometric
Radiation (SKR), radiated by an electron cyclotron resonance above the atmosphere
up a few Saturn's radii (Rs). Previous studies have identified a large scale conjugacy
between radio and UV, as well as IR and UV auroral emissions. Here, we investigate
two days of observations of Saturn's aurorae at radio, UV and IR wavelengths, by the
Cassini RPWS, UVIS and VIMS instruments, and their relationship with a reservoir of
equatorial energetic particles mapped by energetic neutral atoms (ENA), as
measured by MIMI-INCA. This interval of time reveals a series of regular SKR
modulations at the southern SKR phase, and interestingly includes an unusual (but still
regular) enhancement of the auroral activity observed simultaneously at all
wavelengths. This event is likely to illustrate a (regular) nightside injection of energetic
particles, possibly induced by a plasmoid ejection, and then co-rotating with the
planet at the southern SKR period, while feeding an extended longitudinal sector of
intense aurorae. We analyze quantitatively complementary informations brought by
all datasets in terms of energy budget transferred to auroral regions, as well as
magnetospheric dynamics, in order to address the nature and the scheme of Saturn's
rotational modulation.
MOP2011-P0132
Either (Contributed)
3D Multi-fluid Modeling of Ion-neutral Interactions in Titan's Ionosphere
Snowden, D. [1], R. Winglee [2] and R. Yelle [1]
[1] University of Arizona, Lunar and Planetary Laboratory
[2] University of Washington, Earth and Space Sciences
A 3D multi-fluid model of Titan's interaction with Saturn's magnetosphere which
includes three ion and two neutral species is used to study the coupling of ion and
neutral fluids near Titan's exobase. The neutral fluids in Titan's ionosphere are ionized
through photoionization, impact from magnetospheric electrons, and charge
exchange interactions with ions in the ionosphere. Ions are lost through dissociative
recombination, charge exchange, and ion outflow. Ions are accelerated near the
exobase due to Titan's interaction with Saturn's magnetosphere and exchange heat
and momentum with neutral fluids. Using this model we quantify the effect of
ion-neutral collisions on the properties of Titan's plasma interaction near and below
Titan's exobase by comparing model results with and without ion-neutral collisions and
with and without neutral winds.
The acceleration of low-energy ions near Titan's
exobase is affected by the properties of Saturn's magnetosphere; therefore, we
investigate the coupling of ion and neutral fluids near Titan's exobase for several
space environments.
MOP2011-P0035
Either (Contributed)
Simulating the effect of rapid rotation on the local time dependence of
Jupiter's plasma sheet thickness
Vogt, M.F.[1,2], M.G. Kivelson [1,2,3], K.K. Khurana [1] and R.J. Walker [1,2]
[1] Institute of Geophysics and Planetary Physics, UCLA
[2] Department of Earth and Space Sciences, UCLA
[3] Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan
Observations show that Jupiter's plasma sheet is thinnest in the post-midnight to dawn
local time sectors, thickens as it rotates through the morning sector through noon, and
becomes thickest near dusk [Kivelson and Khurana, 2002]. The plasma sheet heating
and thickening near noon can be explained as a response to increased pressure from
the solar wind, as the magnetopause distance decreases by ~50 percent from dawn
to noon. However, one might then expect that the plasma sheet would thin in
response to the reduced solar wind pressure as the magnetopause distance increases
from noon to dusk, but observations show that the opposite is true, and that the
plasma sheet is actually thickest near dusk. These local time asymmetries have been
explained theoretically by Kivelson and Southwood [2005]. They attributed the dusk
side plasma sheet heating and thickening to centrifugal forces due to Jupiter's rapid
rotation, suggesting that as a result of rotation, low energy particles gain parallel
velocity as they move radially outward, and the resulting anisotropy makes the
plasma sheet become unstable. We are developing a large-scale kinetic (LSK)
[Ashour-Abdalla et al., 1993] simulation to test the key physical processes in this idea
that rotation and field line stretching can produce an increase in net energy and
particle anisotropy. In this simulation the Jovian magnetic field is represented by a
simplified, axisymmetric version of the Khurana [1997] field, which we vary in time to
reproduce the stretching that occurs as field lines rotate from noon to dusk. Here we
will present the most recent results from this simulation project.
MOP2011-P0050
Either (Contributed)
Plasma and Magnetic Periodicities in Saturn's Equatorial Ring Current
Ramer, K.M.[1], M.G. Kivelson [1,2], N. Sergis [3], K.K. Khurana [1] and R.J. Walker [1]
[1] IGPP, UCLA
[2] AOSS, University of Michigan
[3] Office for Space Research and Technology, Academy of Athems
Using data taken by the Cassini MAG instrument in 2005 and 2006, we find that
magnetic pressure in the equatorial plane between 6 and 15 Rs oscillates at the SLS4
South frequency, with a second component that falls near the SLS4 North frequency.
Similarly, we are able to identify weak but consistent signatures of both the SLS4N
frequency and the SLS4S frequency in the total ion pressure and inertial forces in
Saturn's equatorial region.
We apply the spectrum analysis technique adopted by
Gurnett et al. [2007], by fitting a sine wave to the measured parameter of interest and
sweeping a range of periods to identify the periods for which the sine fit has the
largest amplitude. We test whether these frequencies also organize electron density,
and partial H+ and O+ pressures. In this presentation we expand our initial study,
which used the data from the equatorial passes in 2005-2006, to include the more
recent equatorial orbits in 2009-2010.
This interval is of particular interest, as it
coincides with the equinox and the subsequent cross-over in the SLS North and South
frequencies, as reported by Gurnett [2009] and Lamy [2010].
MOP2011-P0057
Either (Contributed)
The water vapor plumes of Enceladus
Dong, Y. [1], T. Hill [1], B. Teolis [2], B. Magee [2] and H. Waite [2]
[1] Physics & Astronomy Department, Rice University
[2] Space Science & Engineering Division, Southwest Research Institute
The Cassini E3, E5 and E7 encounters with Enceladus probed the south polar plumes,
where the Ion and Neutral Mass Spectrometer (INMS) measured neutral H2O
molecular densities up to ~109 cm-3. We have constructed a physical model for the
expected water density in the plumes, based on supersonic radial outflow from one or
more of the surface vents. We apply this model to possible surface sources of water
vapor associated with the multiple jets observed in the visible dust plumes (Spitale and
Porco, 2007). Our model predictions fit well with the INMS measurements along the E3,
E5 and E7 trajectories with consistent model parameters. It can also simulate the
fine-scale jet features within the plume observed during the E7 encounter close to
Enceladus' surface. We use E7 data to infer possible source locations for these jets.
MOP2011-P0089
Either (Contributed)
A Survey of Atypical Injection Events in Saturn's Inner Magnetosphere
Kanani, S.J.[1,2], G.H. Jones [1,2], G.R. Lewis [1,2], A.N. Fazakerley [1], C.S. Arridge
[1,2], M.F. Thomsen [3], A.J. Coates [1,2] and F.J. Crary [4]
[1] UCL, Mullard Space Science Laboratory
[2] UCL/Birkbeck, Centre for Planetary Sciences
[3] Los Alamos National Laboratory, Space and Atmospheric Sciences
[4] Southwest Research Institute, Space Science and Engineering
Injections of interchanging flux tubes in Saturn's magnetosphere have been observed
between L = 3 to L = 13 RS and have previously been reported on by many authors
(e.g. Burch, Hill, Mauk [all 2005] etc.).
Studies of injection events have examined
source locations and ion and electron energy-time dispersion profiles but, as yet, a
direct determination of the radial direction of the plasma flow towards or away from
Saturn has not been formulated.
The successful determination of these radial flow
directions would be a useful extension of the observational evidence concerning
these events, particularly in terms of plasma circulation patterns in the kronian
magnetosphere.
We present case studies of several injection events observed by
the Cassini Plasma Spectrometer. By re-examining the electron and ion data we seek
to test previous interpretations of these events, specifically the assessment of how the
flux tubes are moving.
MOP2011-P0102
Either (Contributed)
Uncovering Local Magnetospheric Processes Governing the Variability of
Ganymede's Aurora Using 3D Multi-Fluid Simulations of Ganymede's
Magnetosphere
Payan, A. [1], C. Paty [1] and K. Retherford [2]
[1] Earth and Atmospheric Sciences, Georgia Institute of Technology
[2] N/A, Southwest Research Institute
The electrodynamic interaction of Ganymede's mini-magnetosphere with Jupiter's
fast co-rotating plasma has been shown to give rise to strong current systems closing
not only through the moon and its ionosphere but also through its magnetopause and
magnetotail current sheets. This interaction is strongly evidenced by the presence of
aurorae at Ganymede and of a bright auroral footprint in Jupiter's ionosphere,
referred to as the Ganymede footprint, located equatorward of the main auroral
emissions, at the magnetic longitude of the field line threading Ganymede. The
auroral footprint brightness and latitudinal position have been shown to depend on
the position of Ganymede relative to the Jovian plasma sheet and on the variations of
the current flowing in the current sheet. Previous studies based on ultraviolet images of
Ganymede's auroral footprint at Jupiter obtained with the Hubble Space telescope
(HST) have demonstrated that the size of the auroral footprint was not limited to that
of Ganymede. Rather, it mapped to a region around the satellite extending about 8
to 20 Ganymede radii. Ganymede's auroral footprint brightness was also shown to be
characterized by variations of three different timescales: 5 hours, 10-40 minutes, and
~100 seconds (Grodent et al., JGR, 2009). The goal of the present study is to examine
the relationship between the longest and the shortest timescale periodicities of
Ganymede's auroral footprint brightness and local processes occurring at Ganymede,
using a 3D multi-fluid simulation model. This model allows characterizing the
interaction between Ganymede's magnetosphere and the local Jovian plasma
environment by tracking the energies and fluxes of energetic particles precipitating
into Ganymede's atmosphere. This information can be used to understand the
dynamics of Ganymede's magnetosphere in response to varying upstream Jovian
magnetospheric conditions and to forcing from the co-rotating Jovian plasma
responsible for the fluttering of the plasma sheet over Ganymede. This information
further provides insight into the morphology and the time variability of Ganymede's
aurora resulting from bursty reconnections at Ganymede's magnetosphere.
The
above study will therefore enable determining a likely correlation between the
variability of Ganymede's auroral footprint on Jupiter's ionosphere and the variability
in brightness and morphology of the aurora at Ganymede viewed with HST. This is
done by analyzing the energy distribution of electrons precipitating into Ganymede's
ionosphere and dissociating its molecular oxygen atmosphere with respect to time
and space, as a proxy for the variability of the aurora at Ganymede and the
repartition of the emitted power.
MOP2011-P0062
Poster (Contributed)
Auroral signatures of injections in the magnetosphere of Saturn
Radioti, A. [1], E. Roussos [2], D. Grodent [1], J. Gerard [1], N. Krupp [2], J. Gustin [1], B.
Bonfond [1] and W. Pryor [3]
[1] Laboratory of Atmospheric and Planetary Physics, University of Liege
[2] Planetary Department, Max-Planck-Institut for Solar Sytem Research
[3] Science Department, Central Arizona College
We present auroral features located equatorward of the main auroral ring of emission
at Saturn, which is associated with the open closed field line boundary. Based on
data obtained by the UVIS instrument onboard Cassini, we analyse sequences of
equatorward auroral features and we demonstrate that the corotating features are
elongated with time and their longitudinal intensity distribution is evolving in a
structured way. We compare our observations with simulated injected populations in
the magnetosphere and we demonstrate that the corresponding energy flux is
structured in longitude as the population drifts around the planet in accordance with
the observed auroral features. Additionally, we perform a statistical analysis of the
equatorward auroral features. We show that they magnetically map to an equatorial
source region which ranges from 8 to 18 Rs. Some of the features depart in the vicinity
of the main ring, implying a relation to injected plasma directly from the reconnection
region while others originate several degrees equatorward of main emission.
Properties such as their size, velocity and location are presented and compared with
the properties of the injection events in the magnetosphere of Saturn, observed by
various instruments onboard Cassini.
MOP2011-P0085
Poster (Contributed)
Modeling of Energetic Proton Profiles at Saturn
Kollmann, P. [1,2], E. Roussos [1], C. Paranicas [3], N. Krupp [1] and K. Glassmeier
[1,2]
[1] Solar System Research, Max-Planck-Institute
[2] Institute for Geophysics and Extraterrestrial Physics, Technical University Braunschweig
[3] Applied Physics Laboratory, Johns Hopkins University
Energetic charged particles can undergo a number of different effects in Saturn's
magnetosphere. Some of these processes are well known, as the loss of ions due to
charge exchange within the extended Neutral Torus. On average, these losses have
to be compensated by source processes, but the mechanism and magnitude of
them is poorly understood.
For more than six years now, the MIMI/LEMMS instrument onboard the Cassini
spacecraft has provided a wealth of knowledge about charged particles between
several 10keV and several 10MeV. From this data, mission averaged proton profiles at
constant adiabatic invariants are derived within the radiation belts (L<5R S) and the
middle magnetosphere (L>5RS). We extended the radial diffusion equation by multiple
source and loss terms in order to include all the relevant physics. Numerical solutions of
this equation are able to reproduce the observed profiles. Due to the large number of
effects, the equation includes parameters that are free as long as only a small range
in energy and L is considered. Therefore, we aim to describe the whole range that is
covered by LEMMS with the same set of parameters, which then can immediately be
used to quantify the different effects they are representing and to constrain their
relative importance.
MOP2011-P0014
Poster (Contributed)
Structured Ionospheric Escape at Titan: RPWS/LP, MAG and ELS
Measurements
Edberg, N. [1], K. ?gren [1], J. Wahlund [1], M. Morooka [1], D. Andrews [2], S.
Cowley [2], A. Wellbrock [3], A. Coates [3], C. Bertucci [4] and M. Dougherty [5]
[1] Swedish Institute of Space Physics, Swedish Institute of Space Physics
[2] Dept. of Physics and Astronomy, University of Leicester
[3] MSSL, University College London
[4] Institute for Astronomy and Space Physics, University of Buenos Aires
[5] The Bl
Recent results obtained from measurements by the Cassini Radio and Plasma Wave
Science/Langmuir probe (RPWS/LP), magnetometer (MAG) and electron sensor (ELS)
instruments are presented. We observe a structured region of ionospheric plasma
escaping from the induced magnetosphere of Titan. During the final three of the five
consecutive and similar Cassini Titan flybys T55 - T59, a region characterized by high
electron densities (1-8 cm-3) in the tail/night side of Titan is crossed. Both light and
heavy ions with ionospheric composition are observed to move away from Titan in this
region as observed by CAPS/IMS. This region is observed progressively farther downtail
from pass to pass and is interpreted as a plume of ionospheric plasma escaping Titan,
which appears steady in both location and time. It extends to at least 6 Titan radii
downstream of the moon. Magnetic field measurements indicate the presence of a
current sheet at the inner edge of this region. We suggest that the mechanisms
behind this outflow could be ambipolar diffusion, magnetic moment pumping or
dispersive Alfv?n waves.
MOP2011-P0024
Poster (Contributed)
Global Stress Balance of the Jovian Magnetotail
Vasyliunas, V.M.[1]
[1] -, Max-Planck-Institut fuer Sonnensystemforschung
The defining property of a magnetotail is the existence of a net magnetic tension
force on its inner boundary (facing the planet). The total force on the entire volume of
the
magnetotail
must
be
essentially
zero,
because
the
magnetotail
is
quasi-permanent (not blown away), hence not accelerated, and the enclosed mass
is too small for gravity to balance any applied force (only the planet itself is sufficiently
massive to sustain a net force from the magnetosphere/solar-wind system, the force
being balanced by the gravitational field of the Sun). The total force on any volume
can always be expressed as the total (mechanical plus magnetic) stress tensor
integrated over the enclosing surface. The net sunward magnetic tension force, given
by the integral of the Maxwell stress tensor over the inner boundary of the magnetotail,
must therefore be balanced by a net antisunward force over the rest of the enclosing
surface (consisting of the flanks plus the distant downstream boundary). The magnetic
contribution to this balancing force can be made negligibly small by choosing the
flanks surface just outside the magnetopause and the downstream boundary beyond
the termination of the ordered magnetic structure. The balancing force must then be
mechanical and is given primarily by rate of mass flow through the magnetotail
multiplied by net change in velocity (antisunward speed slower at outflow than at
inflow). In a magnetically open magnetosphere, the mass flow is through the plasma
mantle and down the tail; the mass flux required to balance the observed terrestrial
magnetotail is an appreciable fraction (1/4 to 1/3) of the solar wind flux through an
area equal to the magnetotail cross-section. At Jupiter, with the mass source at the Io
torus, the question is whether the empirically determined total mass input is sufficient
to maintain the observed Jovian magnetotail. Similar questions
arise about the
torque on the Jovian magnetotail: energy for the magnetosphere is extracted
primarily from Jupiter's rotation by a torque acting on the planet, which means that
angular momentum is transported out of the system.
MOP2011-P0025
Poster (Contributed)
Self-sustaining Axial Asymmetries in the Thermosphere as a Driver of
Rotational Periodicities in the Magnetosphere
Smith, C. [1,2] and N. Achilleos [2]
[1] Physics Department, The Brooksbank School
[2] Department of Physics and Astronomy, University College London
The
rotational
magnetosphere
periodicities
observed
in
various
exhibit several puzzling aspects,
phenomena
in
particular
in
Saturn's
the
different
periodicities in the northern and southern hemispheres that appear to have a
seasonal dependence. We explore a possible mechanism for originating the
periodicities in the thermosphere. Our model is based on a feedback effect between
thermospheric winds and heating from particle precipitation. The feedback effect is
shown to be able to permanently break the axisymmetry of the thermosphere,
leading to independent rotating asymmetries in the wind-driven current systems in
each hemisphere. We show using a simple model that the period of these rotating
asymmetries varies with the heating and conductance in each hemisphere,
qualitatively explaining the observed seasonal dependence. We also suggest that the
delay of several months observed in the seasonal dependence could be explained
by long chemical timescales in the upper and middle atmospheres introducing a
corresponding delay in the response of the ionospheric conductance.
MOP2011-P0031
Poster (Contributed)
Studies of the Infrared Aurora by Very High-Resolution Spectroscopy of
Stratospheric Trace Species
Sonnabend, G. [1], M. Sornig [2], D. Stupar [1] and T. Stangier [2]
[1] University of Cologne, I. Physikalisches Institut
[2] University of Cologne, Rheinisches Institut f?r Umweltforschung / Abteilung Planetenforschung
Polar aurorae in Jupiter's atmosphere radiate throughout the electromagnetic
spectrum from X-ray through mid-infrared (mid-IR, 5-20 μm wavelength). Enhanced
emission of ethane molecules in Jupiter's northern auroral region around 11.6 μm has
been detected by means of infrared-heterodyne spectroscopy since many years and
a connection of emission intensity of these molecules to solar activity has been
suggested. Recent developments in technology have now opened additional
wavelength regions to the application of this ultra-high resolution spectrosocpic
method. Using quantum-cascade lasers as local oscillators the Cologne Tuneable
Heterodyne Infrared Spectrometer (THIS) can now be applied to study fully resolved
line profiles of methane and acetylene. Due to the differences in abundance and
photochemical behaviour we hope to gain new insights to the processes in the
stratosphere. First observations are planned beginning 2012 and are to be expected
to coincide with the next solar maximum. An intended long term study will provide
further information on the suggested relationship between solar activity and infrared
auroral emission. We will present sensitivity studies as well as background information
on the observing technique.
MOP2011-P0032
Poster (Contributed)
Anticipating Juno: Mission to Jupiter's Poles
Bagenal, F. [1] and M.W. Group [2]
[1] University of Colorado, APS/LASP
[2] Juno, Mission
The Juno spacecraft arrives at Jupiter in October 2016, entering a polar orbit with a
periapsis of ~1.1 Jupiter radii. Over 33 orbits, Juno will offer unprecedented coverage
of Jupiter's high-latitude auroral regions. In anticipation of Juno, we have followed the
spacecraft trajectory through an empirical magnetic field model (Khurana and
Schwarzl 2005), tracing the intersected field lines to the planet. This mapping provides
the surface field strength, the location of the foot of the magnetic flux tube at the
planet, and the expected loss cone observed at the spacecraft,
providing insight
and planning support for the upcoming Juno mission. We show that the Juno
trajectory crosses many auroral flux tubes by comparing the location of the foot of the
intersected flux tube with the location of the statistical main aurora.
MOP2011-P0037
Poster (Contributed)
Long Term Analysis of Jupiter's DAM Sources
Higgins, C. [1], J. Timmons [1] and F. Reyes [1]
[1] Middle Tennessee State University, Physics & Astronomy
[2] University of Florida, Astronomy
Synoptic observations of Jupiter decametric radio emissions (DAM) were recorded at
the University of Florida Radio Observatory from 1957 to 2007. Occurrence probability
graphs of fixed frequency data at 18, 20, and 22 MHz are shown as a function of
Jupiter central meridian longitude (CML). The Io A, Io B, and Io C source positions are
measured and plotted as a function of time to determine any changes in position and
occurrence probability. Geometrical observational effects have been minimized and
the positions of each source and their errors are calculated. We place upper limits on
the long-term drifting of any sources.
MOP2011-P0039
Poster (Contributed)
Saturn's Magnetosphere: Cassini CAPS Observations
Wilson, R.J.[1] and F. Bagenal [1]
[1] LASP, University of Colorado Boulder
We have derived ion plasma properties by forward-modeling Cassini CAPS
observations throughout the Saturnian magnetosphere (utilizing available PDS data,
through 2009). Anisotropic Maxwellian distributions of OH + and H+ were fit to the data
wherever possible, incorporating local magnetic field observations and a complex
simulation of the CAPS instrument.
We present plasma properties determined with a robust analysis of their uncertainties.
This extensive dataset allows us to explore spatial and temporal variations in
magnetospheric properties, including changes in plasmasheet profiles of density over
the years and evaluation of any super-corotation as potential signatures of return-flow.
MOP2011-P0040
Poster (Contributed)
Short-term Changes in Jupiter's Synchrotron Radiation Caused by
Enhanced Radial Diffusion Driven by Solar UV/EUV Heating
Tsuchiya, F. [1], H. Misawa [1] and A. Morioka [1]
[1] Tohoku University, Graduate School of Science
The total flux density of Jupiter's synchrotron radiation (JSR) at 325 MHz was observed
in 2007 with the Iitate Planetary Radio Telescope (IPRT) to investigate short-term
variations in Jupiter's radiation belt with a time scale of a few days to a month. The
total flux density showed a series of short-term increases and subsequent decreases.
The variations in JSR and the Mg II solar UV/EUV index showed positive correlations, but
the variations in JSR were preceded by those of the Mg II index by 3 to 5 days. The
positive correlation supports a theoretical prediction that an enhancement in the
radial diffusion driven by thermospheric winds in the upper atmosphere causes
changes in relativistic electron distributions in both the radiation belt and the total flux
density of JSR. The radial diffusion model was used to examine the hypothesis that
temporal changes in the radial diffusion rate could be an origin of the short-term
variation. The model includes physical processes such as radial diffusion, energy
degradation by the synchrotron radiation, and several loss processes. We applied a
radial diffusion coefficient of 3×10-8L3/sec, and found a suitable solution that
accounted for both the time scale of the short-term variations and the 4-day time lag.
The model also showed that strong electron loss processes other than the synchrotron
radiation are needed to explain the electron distribution in low L regions. An empirical
electron distribution model showed that the synchrotron radiation does not act as a
loss of electrons in such areas.
MOP2011-P0055
Poster (Contributed)
Whistler-Mode Chorus Enhancements and Anisotropic Electrons in the
Jovian Inner Magnetosphere
Katoh, Y. [1], F. Tsuchiya [2], Y. Miyoshi [3], A. Morioka [2], H. Misawa [2], R. Ujiie [4], W.
Kurth [5], A. Tomas [6] and N. Krupp [7]
[1] Graduate School of Science, Department of Geophysics, Tohoku University
[2] Graduate School of Science, Planetary Plasma and Atmospheric Research Center, Tohoku
University
[3] Solar-Terrestrial Environment Laboratory, Nagoya University
[4] N/A, JAXA
[
We reveal a close relationship between enhancements of whistler-mode chorus and
development of energetic electron anisotropies in the Jovian inner magnetosphere
by conducting a statistical survey of both wave and particle observations of the
Galileo spacecraft. We studied the spatial distribution of intense chorus emissions in
the Jovian magnetosphere and identified 104 chorus enhancements by analyzing
plasma wave data in the frequency range from 5.6 Hz to 20 kHz obtained from the
entire Galileo mission in the inner Jovian magnetosphere during the time period from
December 1995 to September 2003. Enhanced chorus emissions with integrated wave
power over 10-9 (V/m)2 were observed around the magnetic equator in the radial
distance range from 6 to 13 R J. A survey of energetic particle data in the energy
range of 29 to 42 keV reveals that all of the identified chorus events were observed in
the region of pancake pitch angle distributions of energetic electrons. Using empirical
plasma and magnetic field models, we estimate that the ratio of the electron plasma
frequency to the electron cyclotron frequency in this region is in the range from 1 to
10 which is suitable for efficient whistler-mode wave generation. The present study
reveal the statistically significant correspondence between intense chorus and flux
enhancement of energetic electrons having pancake pitch angle distributions in the
Jovian magnetosphere.
MOP2011-P0059
Poster (Contributed)
Solar Wind Response of Jupiter's Magnetosphere Viewed From Radio
Spectrum Analyses
Misawa, H. [1], F. Tsuchiya [1] and A. Morioka [1]
[1] Tohoku University, Planet. Plasma Atmos. Res. Cent.
It is well known that aurorae and auroral radio emissions in the earth are primarily
driven by interaction between the solar wind and the magnetosphere, while in case
of Jupiter, it is thought that some internal processes, probably initiated by the rapid
planetary rotation, primarily drive the auroral activity and the solar wind is a limiting
control parameter. There are many in situ and remote observations support the idea,
however, the role of the solar wind to the magnetic phenomena and pure
characteristics of internal processes have not been revealed well.
In order to
investigate characteristics of the solar wind and non solar wind controls on Jupiter's
magnetic activities in detail, occurrence characteristics of Jupiter's radio emission,
particularly in the hectometric wave range (HOM) observed with WIND/WAVES, have
been analyzed. The analysis period is selected for June to September in 2008, when
the solar activity was considerably calm and predicted solar wind condition at Jupiter
was stable and also showed clear periodicity synchronized with the solar rotation. The
results show that there are 3 types of HOM for the response of solar wind pressure
variations: 1) solar wind related HOM, 2) anti-solar wind related and short lived HOM,
and 3) non solar wind related and quasi-periodic HOM. This implies that the solar wind
is a trigger of Jupiter's magnetic phenomena which activates the phenomena in both
increasing and decreasing periods of the solar wind pressure, and that the activated
regions are different for the two periods.
Acknowledgement:
We would greatly
appreciate M. Kaiser, J.-L. Bougeret and the WIND/WAVES team for providing the
radio wave data.
MOP2011-P0073
Poster (Contributed)
Cassini UVIS Observations of Varying Auroral Emissions on Saturn's Night
Side
Pryor, W.R.[1,2], L. Esposito [3], A. Jouchoux [3], F. Crary [4], U. Dyudina [5], A.
Ingersoll [5], J. Gerard [6], D. Grodent [6], J. Gustin [6] and K. Radioti [6]
[1] Science Dept., Central Arizona College
[2] Planetary and Space Sciences, Space Environment Technologies
[3] LASP, University of Colorado
[4] Space Science, Southwest Research Institute
[5] Geological and Planetary Sciences, Caltech
[6] LPAP, Universit
Cassini UVIS night-side observations from 2009 days 279-281 were obtained with the
UVIS long slit aligned E-W with Saturn's northern auroral oval. This arrangement
provides spatial information in the E-W direction.
Variable spots of UV emission were
observed to rotate across the night side.
The spots vary in brightness
quasiperiodically with brightness peaks separated by several tens of minutes.
These
observations were coordinated with an ISS auroral movie that also shows episodic
emission features.
We will compare these observations and examine the
spectroscopy of the emission features. The spectroscopy constrains the energy of
the precipitating electrons.
MOP2011-P0075
Poster (Contributed)
The Ultraviolet Spectrograph (UVS) on Juno
Gladstone, G.R.[1], S. Persyn [1], J. Eterno [1], D.C. Slater [1], M.W. Davis [1], M.H.
Versteeg [1], K.B. Persson [1], B. Walther [1], B. Trantham [1], O.H. Siegmund [2], J.V.
Vallerga [2], B. Marquet [3], F. Denis [3], J. G?rard [4] and D.C. Grodent [4]
[1] Space Science, Southwest Research Institute
[2] Engineering, Sensor Sciences
[3] Engineering, Centre Spatial de Li?ge
[4] Laboratoire de Physique Atmospherique et Planetaire, Universit? de Li?ge
Juno, a NASA New Frontiers mission, plans for launch in August 2011, a 5-year cruise
(including an Earth flyby in October 2013 for a gravity boost), and 14 months around
Jupiter after arriving in July 2016. The spinning (2 RPM), solar-powered Juno will study
Jupiter from a highly elliptical orbit, in which the spacecraft (for ~6 hours once every
11 days) dives down over the north pole, skims the outermost atmosphere (at altitudes
of 3500-5000 km), and rises back up over the south pole. This orbit allows Juno avoid
most of the intense particle radiation surrounding the planet and provides an
excellent platform for investigating Jupiter's polar magnetosphere. Juno will carry an
Ultraviolet Spectrograph (UVS) to make spectral images of Jupiter's aurora. UVS is a UV
imaging spectrograph sensitive to far ultraviolet emissions in the 70-205 nm range that
will characterize both the morphology and spectral nature of Jupiter's auroral
emissions.
Juno
UVS
telescope/spectrograph
consists
of
assembly
two
and
separate
a
vault
sections:
a
electronics
dedicated
box.
The
telescope/spectrograph assembly contains a telescope which feeds a 0.15-m
Rowland circle spectrograph. The telescope has an input aperture 40 x 40 mm 2 and
uses an off-axis parabolic primary mirror. A flat scan mirror situated at the front end of
the telescope (used to target specific auroral features at up to ±30° perpendicular to
the Juno spin plane) directs incoming light to the primary. The light is then focused
onto the spectrograph entrance slit, which has a dog-bone shape 6° long, in three 2°
sections of 0.2°, 0.05°, and 0.2° width (projected onto the sky). Light entering the slit is
dispersed by a toroidal grating which focuses the UV bandpass onto a curved
microchannel plate (MCP) cross delay line (XDL) detector with a solar blind
UV-sensitive CsI photocathode,
which makes up the instrument's focal plane.
Tantalum shielding surrounds the detector assembly to protect the detector and the
adjacent detector electronics from high-energy electrons. The main electronics box is
located in the Juno vault. Inside are two redundant high-voltage power supplies
(HVPS), two redundant low-voltage power supplies, the command and data handling
(C&DH) electronics, heater/actuator activation electronics, scan mirror electronics,
and event processing electronics. An overview of the UVS design and expected
scientific performance will be presented.
MOP2011-P0076
Poster (Contributed)
Comparing the region of Solar Wind influence in Jupiter's auroral region
with current magnetospheric models.
Stallard, T. [1], H. Melin [1] and S. Miller [2]
[1] Physics and Astronomy, University of Leicester
[2] Physics and Astronomy, University College London
The region poleward of the main auroral emission of Jupiter remains a matter of
significant research and debate, with several models investigating the potential
magnetospheric origin of the auroral features seen there. One important piece of
evidence about this magnetospheric origin comes from measurements of ion winds
within the ionosphere.
In a past study, Stallard et al. (2003) identified a region of
stagnant flow within the ionosphere, as measured in the inertial frame, showing the
direct influence of the solar wind on the upper atmosphere.
This region, described as
the 'fixed Dark Polar Region' (f-DPR) was flanked on the dawn and equatorward sides,
inside the main emission, by a region of flow that was sub-corotating at varying
degrees relative to the planet, not held completely at a zero inertial velocity. This was
described as the 'returning Dark Polar Region' (r-DPR).
Subsequent observations of
the UV polar morphology strongly suggested that the UV brightness had matching
regions inside the main auroral emission: the r-DPR matching with the Dark Region and
the f-DPR matching with the Swirl Region.
However, recent models (Vogt et al. and
Alexeev et al.) of the open field line region (one of two major theories for the origin of
the solar wind influence in Jupiter's pole) have strongly suggested that the open-close
field line boundary does not map to the boundary between the Dark Region and the
Swirl Region, but in fact lies somewhere within the Dark region. Here, we re-examine
the original velocity measurements, directly comparing them with the modelled
velocity flow expected from models of the projection of the open-close field line
boundary into Jupiter's auroral region, as would be seen through the Earth's
atmosphere.
MOP2011-P0081
Poster (Contributed)
Comparative Planetary Magnetotails
Bagenal, F. [1], C. Jackman [2], J. Slavin [3], M. Vogt [4], C. Arridge [5], X. Jia [6], S.
Milan [7], M. Freeman [8] and A. Walsh [5]
[1] APS/LASP, University of Colorado
[2] Space Physics, University College
[3] Heliophysics, Goddard Space Flight Center
[4] IGPP, UCLA
[5] Mullard Space Science Lab, University College
[6] Atmospheric Sciences, University of Michigan
[7] Space Sciences,
We compare the magnetotails of
the outer planets Jupiter and Saturn with the
magnetotails of the terrestrial planets Earth and Mercury. Specifically, we compare
their scaled
sizes and how their magnetopause standoff distances respond to solar
wind ram pressure. We examine evidence for mass loss down the tail, summarize
estimates of amount of open flux and of the global transport of magnetic flux.
MOP2011-P0082
Poster (Contributed)
Jupiter's Plasmasheet: Voyager and Galileo Observations
Bagenal, F. [1], R. Wilson [1], J. Richardson [2] and W. Paterson [3]
[1] LASP, University of Colorado
[2] Center for Space Research, MIT
[3] Heliophysics, Goddard Space Flight Center
We have collated and, in some cases, re-analyzed the plasma data obtained by the
Voyager 1 & 2 and Galileo spacecraft in the magnetosphere of Jupiter. We present
the derived spatial and temporal variations in plasma density, temperature and
velocity throughout the plasmasheet. We also use a simple model for density
distribution with latitude to produce 3-D maps of plasmasheet properties and derive
the flow of mass and energy in the magnetosphere.
MOP2011-P0084
Poster (Contributed)
Statistical properties of the magnetic field in the kronian magnetotail
lobes and current sheet.
Jackman, C.M.[1] and C.S. Arridge [2,3]
[1] Department of Physics and Astronomy, University College London
[2] Mullard Space Science Laboratory, University College London
[3] The Centre for Planetary Sciences, UCL/Birkbeck
We examine the characteristics of the magnetic field in Saturn's magnetotail lobes
and current sheet during the Cassini spacecraft's exploration of the magnetotail from
day 18-291 of 2006. During this period Cassini reached maximum downtail distances of
~68 RS, with orbits at the beginning of the survey interval concentrating on the
equatorial regions, while later orbits moved to somewhat higher latitudes. We find the
field strength in the lobes falls off as Blobe (nT) = (251 &plusmn 22) &times (r (RS)) -1.20
&plusmn 0.03.
We show that the lobes and current sheet have distinctive magnetic
pressure distributions, and we examine the transition of the field from the central
current sheet out into the northern and southern lobes.
MOP2011-P0092
Poster (Contributed)
Seasonal variability in the ionosphere of Uranus
Melin, H. [1], T. Stallard [1], S. Miller [2], L.M. Trafton [3], T. Encrenaz [4] and T.R.
Geballe [5]
[1] Department of Physics & Astronomy, University of Leicester
[2] Atmospheric Physics Laboratory, University College London
[3] Department of Astronomy, University of Texas
[4] CNRS-UMR, LEISA
[5] Gemini Observatory, Gemini Observatory
Ground based infrared observations of the H3+ ionosphere of Uranus, spanning 16
years, have been analysed as to identify any long-term trends in the temperature and
density of the uranian ionosphere. Between 1992 and 2008, the temperature is seen
decreasing by 8 K per year, between 715 K and 534 K. With equinox occurring in 2007,
the cooling of the atmosphere appears linked to seasonal geometry with respect to
the Sun, even though the Sun alone does not provide enough energy to heat the
planet to the observed temperatures. The mechanism that is responsible for heating
the planet is therefore likely linked to conductivity, regulated by nightside relaxation of
the ionosphere.
MOP2011-P0095
Poster (Contributed)
Model of Io's Local Interaction: a Coupled MHD-Hall/Chemistry Model
Dols, V. [1], P.A. Delamere [1] and F. Bagenal [1]
[1] University of Colorado, LASP
Past studies have tackled the problem of the local interaction of Io's corona with the
plasma in the torus using different complementary approaches, each providing new
insights in the interaction but also involving some important simplifications.
The MHD
models employ a parameterization of the source of ionization, generally assuming a
spherical symmetry and a single species, generally O and S (Linker et al., 1998; Combi
et al., 1998, Khurana et al., 2011)).
They thus by-pass the important effect of the
cooling of electrons (Saur et al., 1999) and the multi-species chemistry. Others have
taken a 2-fluid approach assuming a constant magnetic field (Saur et al., 1999),
limiting the self-consistency of their approach or made a full hybrid simulation
assuming an unrealistic ion mass to circumvent numerical limitations (Lipatov and
Combi, 2006).
We combine a multi-species chemistry model of the interaction that
includes atomic and molecular species (Dols et al., 2008) with a self-consistent
MHD-HALL calculation of the flow and magnetic perturbation to model as
self-consistently as possible the plasma variables (plasma density, ion average
temperature, composition, velocity, magnetic perturbation) along six different Galileo
flybys of Io and compare to the observations.
MOP2011-P0096
Poster (Contributed)
Magnetosphere-ionosphere Coupling in Jupiter's Middle Magnetosphere:
Computations Including a Self-Consistent Current Sheet Magnetic Field
Model
Nichols, J. [1]
[1] Department of Physics and Astronomy, University of Leicester
In this paper we consider the effect of a self-consistently computed magnetosdisc
field structure on the magnetosphere-ionosphere coupling current system at
Jupiter. ?Specifically, we we incorporate the calculation of the plasma angular
velocity profile using Hill-Pontius theory into the magnetodisc model of Caudal [1986],
such that the resulting magnetosphere-ionosphere currents are computed using
values of the equatorial magnetic field self-consistent with the plasma angular
velocity profile. In doing so we update the model results of Caudal [1986] using more
realistic plasma parameters, including values obtained from Galileo data.
We find
that the azimuthal current intensity, and thus the stretching of the magnetic field lines,
is dependent on the magnetosphere-ionosphere coupling current system parameters,
i.e. the ionospheric Pedersen conductivity and iogenic plasma mass outflow
rate. ?Overall, however, the equatorial magnetic field profiles obtained are similar in
the inner region to those used previously, such that the currents are of the same order
as previous solutions obtained using a fixed empirical equatorial field strength model,
although in the outer region the fringing field of the current disc acts to reverse the
field-aligned current.
We also find that, while the azimuthal current in the inner
region is dominated by hot plasma pressure, as is generally held to be the case at
Jupiter, the use of a realistic plasma angular velocity profile actually results in the
centrifugal current becoming dominant in the outer magnetosphere. In addition,
despite the dependence of the intensity of the azimuthal current on the
magnetosphere-ionosphere coupling current system parameters, the location of the
peak field-aligned current in the equatorial plane also varies, such that the
ionospheric location remains roughly constant.
It is thus found that significant
changes to the mass density of the iogenic plasma disc are required to explain the
variation in the main oval location observed using HST.
MOP2011-P0099
Poster (Contributed)
Initial Results: Coupling Eruptive Dynamics Models to Multi-fluid Plasma
Dynamic Simulations at Enceladus
Paty, C. [1], J.D. Dufek [1], R.L. Tokar [2] and K. Fisher [1]
[1] Georgia Institute of Technology, School of Earth & Atmospheric Sciences
[2] Space and Atmospheric Sciences Group, Los Alamos National Laboratory
The interaction of Saturn's magnetosphere with Enceladus provides an exciting
natural laboratory for expanding our understanding of charge-neutral interactions
and their impact on mass and momentum loading of the system and the associated
magnetic perturbations. However, one of the more challenging questions on the
Enceladus plume relates to the subsurface eruptive mechanism responsible for
generating the observed jets of material that compose the plume. In this work we
implement a multiphase eruptive dynamics model [cf. Dufek & Bergantz, Geochem.
Geophys. Geosyst., 2007] to examine several physical mechanisms that have been
proposed to drive the eruptions, including: pressurized liquid water, gas water mixtures,
and water-ice sublimation. These initial models describing the resulting gas and dust
grain distribution will be presented in the context of existing observations. We will also
demonstrate the first stages of integration of these results into the existing multi-fluid
plasma dynamic simulations of Enceladus' interaction with Saturn's magnetosphere.
These more sophisticated plume morphologies and their effects on the plasma
dynamic interaction will be assessed in the context of existing modeling efforts for this
system.
MOP2011-P0100
Poster (Contributed)
Initial Modeling of a New High-Speed Atmospheric Ejection Process at Io
Schneider, N. [1], C. Grava [2] and C. Barbieri [2]
[1] U. Colorado, LASP
[2] Dipartimento di Astronomia, Universita di Padova
High-resolution spectra of Io sodium have identified an unexpected high- speed
ejection process operating near Io's wake
and Jupiter-facing hemisphere.
Observations in 2007 with the SARG spectrograph on the 3.6-m Telescopio Nazionale
Galileo in the Canary Islands targeted Io as it neared eclipse behind Jupiter. Our
spectra of this region in the hour before eclipse revealed an unexpected signature of
high-speed atmospheric escape distinct from the red-shifted "jet" and "stream"
directed in the ani-Jupiter sense. The new feature is clearly blue-shifted, indicating
ejection from Io towards Jupiter. The observed directionality and speeds exceeding
10 km/sec indicate a source process involving fields and currents in Io's atmosphere
and/or wake, as opposed to the lower speeds and more isotropic ejection expected
from collisions. Preliminary analysis indicates that the source process is not active
immediately after eclipse, suggesting the mechanism is reduced by atmospheric
collapse or the lack of of photoionization. Observations in 2009 confirmed the
Jupiter-directed ejection with Io near superior conjunction with Jupiter. At present
there are no known ejection mechanisms that satisfy the observed properties. We will
present empirical models of the escaping sodium designed to constrain the geometry,
velocity and timing of the escape process in hopes of identifying a causal mechanism
in the plasma interaction at Io. This work has been supported by NSF's Planetary
Astronomy Program, INAF/TNG, Dipartimento di Astronomia, Universita di Padova,
through a contract by the Italian Space Agency ASI.
MOP2011-P0107
Poster (Contributed)
Io's Extended Atmosphere Observed with New Horizons Alice
Retherford, K.D.[1], A.J. Steffl [2] and M.H. Burger [3,4]
[1] Space Science and Engineering, Southwest Research Institute
[2] Space Science and Engineering, Southwest Research Institute
[3] Blank, NASA/GSFC
[4] Blank, Morgan State University
Io's UV auroral and airglow emissions were observed by the New Horizons Alice
instrument in 2007 during the spacecraft's Jupiter encounter. Initial results reported
by Retherford et al., Science, 2007 include analysis of auroral brightness variations
upon eclipse ingress and egress that provide evidence for changes in the relative
contribution of sublimation and volcanic sources in shadow and at night.
Additional
Io observations were obtained with the Alice imaging spectrograph while the satellite
was in sunlight at various solar phase angles and locations within the Io plasma torus.
These data allow a statistically meaningful trending analysis to be performed to better
understand diurnal atmospheric variability. Neutral atomic oxygen and neutral and
ionized atomic sulfur emission brightnesses are determined after subtraction of
background Io plasma torus emission features also present in the Alice data.
Neutral
oxygen emissions are detected out to ~40 RIo, which considerably expands spatial
imaging of these emissions past the ~10 RIo extent of emissions detected with HST/STIS
and reported by Wolven et al., JGR, 2001.
We discuss our results with comparisons to
numerous Earth-based observations of Io's atmosphere obtained with HST/ACS,
HST/STIS, and other instruments. Initial comparisons with exosphere and neutral cloud
models out to the ~40 Io radii regime will also be presented.
MOP2011-P0114
Poster (Contributed)
Cassini End of Mission Model Predictions
Moore, L. [1], I. Mueller-Wodarg [2,1], M. Galand [2,1] and M. Mendillo [1]
[1] Center for Space Physics, Boston University
[2] pace & Atmospheric Physics Group, Imperial College London
In May 2017 the Cassini spacecraft is due to end its remarkably successful mission by
plunging into Saturn's atmosphere.
The nominal goal of such a maneuver is to
prevent any possible biocontamination of Saturn's moons; however, valuable in-situ
information regarding the state of the upper atmosphere may also be retrieved.
Using the Saturn-Thermosphere-Ionosphere Model (STIM), a state-of-the-art global
circulation model developed over the past 8 years, we make predictions for those
final measurements, along the path of Cassini through Saturn's inner plasmasphere,
ionosphere, and thermosphere.
The implications of these predictions are discussed
in terms of their impact on the coupled Saturn magnetosphere-ionosphere system.
MOP2011-P0117
Poster (Contributed)
Active Current Sheets in Saturn's Outer Magnetosphere
Arridge, C. [1,2], A. Coates [1,2], F. Crary [3], M. Dougherty [4], C. Forsyth [1], C.
Jackman [5,2], T. Krimigis [6], N. Krupp [7], L. Lamy [8], E. Roussos [7], N. Sergis [9], J.
Slavin [10] and A. Walsh [1]
[1] Mullard Space Science Laboratory, University College London
[2] The Centre for Planetary Sciences, UCL/Birkbeck
[3] Space Science and Engineering Division, Southwest Research Institute
[4] Department of Physics, Imperial College
[5] Department of Phys
Hot electron distributions are often found in Saturn's plasma sheet and have been
associated with magnetic reconnection in Saturn's outer magnetosphere. Typically
the electrons are at least an order of magnitude more energetic than the surrounding
electron populations and abrupt transitions are observed between the two regimes.
Sometimes these energetic populations are observed as part of a bi-modal
distribution with more typical warm plasma sheet electrons. In this poster we present
case studies of some intervals in Saturn's outer magnetosphere where these hot
electrons are present and examine the surrounding structure. We show significant
changes in the current and plasma sheet on the timescale of hours and disruptions in
the current sheet which appear to persist for more than one rotation of the plasma
sheet around the planet.
MOP2011-P0119
Poster (Contributed)
Variability of Io plasma torus in response to solar wind
Kagitani, M. [1], M. Yoneda [1], F. Tsuchiya [1], S. Okano [1], K. Yoshioka [1] and C.
Tao [1]
[1] Tohoku University, Planetary Plasma and Atmospheric Research Center
[2] Rikkyo University, Department of Physics
[3] JAXA, ISAS
Plasma originated from volcanic eruption on Jovian satellite Io forms a donut-shaped
region of dense plasma along Io's orbit, which is called Io plasma torus. Ions in the
plasma torus, mainly consist of sulfur and oxygen ions, are excited by electron impact
and emit photons in wavelength range from EUV to NIR.
Although timescale of
outward radial transport in the plasma torus region is several tens of days, recent
studies have been reported rapid change of EUV emission from the Io plasma torus,
narrowband kilometric (nKOM) radiation and aurora in response to the solar wind
(Steffl et al., 2004; Plyor et al., 2005; Nozawa et al., 2006; Tsuchiya et al., 2009). In this
study, we report a observational result of quick changes of [SII] 673.1nm and 671.6nm
emissions in response to the solar wind.
The observation was made using
high-dispersion spectrograph with a field-of-view of 5'' by 500'' coupled to 40-cm
telescope at Mt. Haleakala from July through December 2009 in which 560 spectral
datasets were obtained.
Average intensity of [SII] emissions in the ribbon region
changes from 500 to 900 Rayleighs depending on System III longitude.
There are
twelve brightening events in which the emission intensity exceeds more than 1300
Rayleighs.
Five of them are associated with enhancements of solar wind dynamic
pressure at Jupiter, which are expected from the extrapolation of solar wind
measurements at the Earth's orbit.
Considering changes of ion temperature derived
from Doppler width and use of narrow slit compared to latitudinal extent of the Io
plasma torus, it seems to be concluded that the changes of measured emission
intensity are not caused by increase of flux tube content but by decrease of ion
temperature.
MOP2011-P0128
Poster (Contributed)
Electron signatures at Hyperion
Nordheim, T. [1,2], G.H. Jones [1,2], A.J. Coates [1,2], J.S. Leisner [3], W.S. Kurth [3],
K.K. Khurana [4] and F.J. Crary [5]
[1] Mullard Space Science Laboratory, University College London
[2] Centre for Planetary Sciences at UCL/Birkbeck, University College London
[3] Department of Physics and Astronomy, University of Iowa
[4] Institute of Geophysics and Planetary Physics, Uni
Cassini has conducted one targeted flyby of the moon Hyperion, which occurred on
September 26th 2005. When examining data from CAPS-ELS in the time interval
around closest approach, field aligned electron beam signatures were discovered.
The theory that these electrons may be associated with surface processes on the
moon will be discussed in the context of observations made using CAPS. We also
provide an overview of complementary observations by other Cassini instruments.
MOP2011-P0138
Poster (Contributed)
Plan for Observing Magnetospheres of Outer Planets by Using the EUV
Spectrograph Onboard the SPRINT-A/EXCEED Mission
Tsuchiya, F. [1], M. Kagitani [1], N. Terada [1], Y. Kasaba [1], I. Yoshikawa [2], K. Sakai
[2], T. Homma [2], K. Yoshioka [3], A. Yamazaki [4], K. Uemizu [4], T. Kimura [4], G.
Murakami [4], M. Ueno [4]
[1] Graduate School of Science, Tohoku University
[2] Department of Earth and Planetary Science, The University of Tokyo
[3] Department of Physics, Rikkyo University
[4] Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
The EXCEED mission is an Earth orbiting extreme ultraviolet (EUV) spectroscopic mission
and the first in the SPRINT series being developed by ISAS/JAXA. EUV spectroscopy is
suitable for observing tenuous gases and plasmas around planets in the solar system
(e.g., Mercury, Venus, Mars, Jupiter, and Saturn). One of the primary observation
targets is Jupiter, whose magnetospheric plasma dynamics is dominated by
planetary rotation. In the EUV range, a number of emission lines originate from
plasmas distributed in Jupiter's inner magnetosphere. The
EXCEED spectrograph is
designed to have a wavelength range from 55 to 145 nm with minimum spectral
resolution of 0.4 nm, enabling the electron temperature and ion composition in the
inner magnetosphere to be determined. The spectrograph slits have a field of view
of 400x40 arc-seconds (maximum), and an onboard target guide camera is used to
stabilize attitude fluctuations to within +-5 arc-seconds. With a large primary mirror
(diameter: 20 cm) and high detection efficiencies (1 to 3%), EXCEED will measure Io
plasma torus emission distributions with a good S/N using an exposure time of 50
minutes and achieving spatial resolution of 20 arcseconds. The previous observation
of plasmas in the inner magnetosphere and the aurora with an EUV spectrograph was
done by the Cassini spacecraft over a period of a few months. We examined the
data obtained by the UVIS instrument to clarify the scientific objectives for the EXCEED
mission. The UVIS observation sometimes showed sudden brightening in both the
aurora and the Io plasma torus with a timescale from several hours to a few tens of
hours.
From the analysis of the UVIS data as well as radio waves (Cassini/RPWS) and the
interplanetary magnetic field (Galileo/MAG) data, we found that the brightening
events were related to a large scale structure in the solar wind.
However, because the Cassini observations had a lack of continuity due to the
intermittent observation mode, it is difficult to make a definitive relation between the
aurora and the plasma emissions in the inner magnetosphere. EXCEED plans to
observe the variations in the aurora and in the radial structures of plasma emissions
and should reveal the relationship between them in detail. The EXCEED observations
are expected to investigate the radial plasma and energy transport processes in the
rotation-driven magnetosphere.
MOP2011-P0047
Poster (Contributed)
Observational evidence for a conversion of upper hybrid resonances into
electromagnetic modes at the Enceladus plasma torus
Taubenschuss, U. [1], P. Schippers [1], J.S. Leisner [1], G. Fischer [2], D.A. Gurnett [1],
A.M. Persoon [1] and J.B. Faden [1]
[1] University of Iowa, Department of Physics and Astronomy
[2] Space Research Institute, Austrian Academy of Sciences
Several crossings of Cassini through the Enceladus plasma torus show sporadic
intensifications of electrostatic oscillations at the local upper hybrid resonance
frequency. Analysis of the polarization reveals that these intensive emissions become
circularly polarized, in contrast to the unpolarized upper hybrid oscillations. Thus, we
conclude that density gradients at the outer edges of the Enceladus plasma torus
provide appropriate conditions for mode conversion from electrostatic oscillations to
the electromagnetic modes O and/or Z. Events are observed between L-shells of 6 to
10 and up to mid-latitudes. Active mode conversion could also be verified for
interchange events, i.e. inside density depleted magnetic flux ropes. A model for the
generation and beaming pattern is presented which explains how these emissions
could be the source for what is finally seen as Saturn drifting bursts (SDBs) by an
observer at larger radial distances.
MOP2011-P0066
Poster (Contributed)
Io's volcanic effect on Jupiter's megnetospheric activity
Yoneda, M. [1], F. Tsuchiya [1], B. Bonfond [2], T. Miyata [3], H. Misawa [1], M.
Kagitani [1] and S. okano [1]
[1] PPARC, Tohoku University
[2] Laboratoire de Physique Atmosph?rique et Plan?taire, Universit? de Li?ge
[3] Institute of Astronomy, The University of Tokyo
Io is the most volcanically active body in the solar system. Io's atmosphere consists of
volcanic gas, and this volcanic gas continuously escapes from Io into Jupiter's inner
magnetosphere. Jupiter's inner magnetosphere is therefore occupied by plasma
which consists of heavy ions (e.g., S+, S++, S+++, O+, O++ and O+++). This
magnetospheric environment is very different from that of the earth because its
magnetospheric plasma has its origin almost only in solar wind. It is well-known that
magnetospheric phenomena of the earth like magnetic storms are actually triggered
or controlled by the solar wind or solar activity. Influence of the solar wind on Jupiter's
magnetosphere is also known. However, Io's contribution on Jupiter's magnetospheric
changes has not investigated well while we know Jupiter's inner magnetosphere is
filled with Iogenic plasma. In this study, we tried to reveal this outstanding issue.
Jupiter's sodium nebula, extending over several hundreds of Jovian radii, is a result of
atmospheric escape of sodium atoms originated from Io through Jupiter's inner
magnetospheric structure called Io plasma torus. A distinct enhancement in the
sodium nebula brightness was seen in 2007. In addition, we found that activity of
Jupiter's radio emissions called HOM had decreased with respect to the sodium
nebula enhancement. The HOM is believed to a radio emission due to aurora activity.
Actually, certain changes in Jupiter's aurora were seen with respect to brightness and
morphology from the Hubble FUV data (see a presentation by Bonfond et al). These
finding may be indicative of Io's volcanic effect on Jupiter's magnetosphere. In
addition to these phenomena in Jupiter's magnetosphere, we are now trying to
making a direct observation of Io's volcanism by means of mid-infrared. Details of our
research and observation activities will be shown in this presentation.
MOP2011-P0072
Poster (Contributed)
Study On Post-Eclipse Brightening Of Io Sodium Cloud
Grava, C. [1], N.M. Schneider [2] and C. Barbieri [1]
[1] University of Padua, Astronomy Department
[2] University of Colorado, LASP
We report results of a study of true temporal variations in Io's sodium cloud before and
after eclipse by Jupiter. The hypothesis we want to test is that the atmosphere partially
condenses when the satellite enters the Jupiter's shadow, preventing sodium from
being released to the cloud in the hours immediately after the reappearance. The
challenge lies in disentangling true variations in sodium content from the changing
strength of resonant scattering due to Io's changing Doppler shift in the solar
Fraunhofer line. We undertook observing runs at the italian telescope TNG at La Palma
Island with the high resolution echelle spectrograph SARG, both before and after
eclipse, in the region around the doublet of sodium, the most easily detectable
element in Io's atmosphere from ground-based observatories. The particular
configuration chosen for the observations allowed us to observe Io close enough to
Jupiter and to disentangle line-of-sight effects looking perpendicularly at the
elongated sodium cloud. The results we present here took advantage of a very
careful reduction strategy. We remove the dependence from heliocentric radial
velocity of Io by dividing the observations for the gamma factor, which is the fraction
of solar light available for resonant scattering. Then we convert the observed photon
intensity, which depends on Io's orbital position, to column abundance, to test
whether it is constant along Io's trajectory. We present column density differences
before and after the eclipse. This work has been supported by NSF's Planetary
Astronomy Program, INAF/TNG and the Astronomy Department of University of
Padova, through a contract by the Italian Space Agency ASI.
MOP2011-P0077
Poster (Contributed)
Variability of SKR modulations and validity of the strobe-like picture
Lamy, L. [1]
[1] Observatory of Paris, LESIA
Among the persistent questions raised by the existence of a rotational modulation of
the Saturn Kilometric Radiation (SKR), the origin of the variability of the 10.8 hours SKR
period at a 1% level over weeks to years remains intriguing. While its short-term
fluctuations (20-30 days) have been related to the variations of the solar wind speed,
its long-term fluctuations (months to years) were proposed to be triggered by
Enceladus mass-loading and/or seasonal variations. This situation has become even
more complicated since the recent identification of two separated periods at 10.8h
and 10.6h, each varying with time, corresponding to SKR sources located in the
southern (S) and the northern (N) hemispheres, respectively. Here, six years of Cassini
continuous radio measurements are investigated, from 2004 (pre-equinox) to the end
of 2010 (post-equinox). From S and N SKR, radio periods and phase systems are
derived separately for each hemisphere and fluctuations of radio periods are
investigated at time scales of years to a few months. Then, the S phase is used to
demonstrate that the S SKR rotational modulation is consistent with an intrinsically
rotating phenomenon, in contrast with the early Voyager picture.
MOP2011-P0135
Poster (Contributed)
North-South asymmetry of Saturn magnetosphere-ionosphere coupling
system
Tao, C. [1], S.V. Badman [1] and M. Fujimoto [1]
[1] JAXA, ISAS
Recent Saturn observations through aurora, radio emission periodicity and magnetic
field
variation
show
magnetosphere-ionosphere
interesting
coupling
north-south
system
inherently
asymmetry.
contains
Saturn
asymmetric
magnetic field and the tilt of rotational axis against ecliptic vertical direction. Sunlit
variation would produce north-south asymmetry of not only ionospheric conductance
but also auroral acceleration, i.e., parallel electric field, through background density
variation. We investigate the north-south asymmetry of magnetosphere-ionosphere
coupling system. Under total magnetospheric electric field is constant as an electric
field generator, ionospheric perpendicular electric field varies with parallel electric
field variation. Variation of the ionospheric electric field affects Joule heating and ion
drag which modify the wind dynamics and thermal field. We would like to discuss how
this effect works and relates with observed hemispheric asymmetries.
MOP2011-P0136
Poster (Contributed)
Non-MHD Aspects of Ganymede's Magnetosphere: Investigation of
Wave-Particle Interaction Based on Multi-Instrumental Observations by
Galileo
Kimura, T. [1], S. Kasahara [1], M. Fujimoto [1] and N. Krupp [2]
[1] Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
[2] The Planets and Comets department, Max Planck Institute for Solar System Research
Basic characteristics of Ganymede's magnetosphere were revealed based on in-situ
measurements by Galileo spacecraft during six encounters (e.g., particle dynamics by
Williams et al. 1997a, b, 1998, 2001, 2004). Recently, global configuration of the
magnetosphere and interaction with Jovian magnetosphere are also intensively
investigated based on MHD simulations (Jia et al., 2009, 2010). However, non-MHD
characteristics of Ganymede's magnetosphere have not been discussed in detail yet.
For example, wave-particle interactions, ion kinetics, and polar field aligned particle
accelerations excited via Jupiter-Ganymede interactions. This study addresses ion
kinetics
and
related
wave-particle
interaction
process
in
Ganymede's
magnetosphere based on multi-instrumental observations Galileo spacecraft. G02
orbit was selected for investigation of Jupiter-Ganymede interactions because only
during this pass Galileo went through the polar cap region where Jovian
magnetosphere and Ganymede's magnetosphere are strongly connecting with each
other. Observations of high and low frequency wave, particle energy spectra, and
pitch angle distribution revealed large amplitude perturbation field at low frequencies
accompanied by strong ion anisotropy with upward directed loss cone above polar
cap. Theoretical consideration about cyclotron resonance process suggested that
these perturbation fields are downward propagating ion-related wave whose
Poynting flux was estimated to be comparable to that of low energy electron kinetic
energy precipitating from Jovian magnetosphere. This suggests significant energy
input of the low frequency waves onto the polar ionosphere of Ganymede, which
could be responsible for ionospheric heating like Earth's polar ionosphere. Universality
of ionospheric heating process at Ganymede, Earth, and Mercury will be discussed in
this presentation.
MOP2011-P0002
Poster (Contributed)
The Role of the Electron Convection Term for the Parallel Electric Field
and Electron Acceleration in the Io-Jupiter System
Matsuda, K. [1], N. Terada [1], Y. Katoh [1] and H. Misawa [1]
[1] Department of Geophysics, Tohoku University
Subcorotation of Iogenic plasma in the Io plasma torus has been understood as
electric drift by a perpendicular electric field with respect to the Jovian magnetic field.
A part of the radially integrated potential has been considered to be imposed along
the magnetic field lines and would cause the Io's trailing tail aurora. The purpose of
this study is to clarify where and how the actual electric fields arise in the Io-Jupiter
system. Here, we take notice of the importance of the electron convection term in
the generalized Ohm's law. We applied a semi-discrete central scheme to extended
MHD equations which include the electron convection term and investigated the role
of the electron convection term for the parallel electric field and electron
acceleration in a one-dimensional model of the Io-Jupiter system.
We find that the
electron convection term works like the gradient of the negative pressure and it
reduces the phase velocity of the ion sound mode. At a steady state discontinuity, the
sum of the ion and electron convection terms balances with the ion pressure gradient.
An electrostatic potential difference across a discontinuity equals the electron kinetic
energy obtained from a transition through the discontinuity. The electron convection
term enables us to describe a situation in which a parallel electric field and parallel
electron acceleration coexist, which is impossible for ideal or resistive MHD. If the
parallel current density exceeds the critical current density, the ion sound mode grows
exponentially. This is the ion acoustic instability described in the fluid frame. If the
sound mode of the cold ions is unstable and that of the hot ions is stable with the
specific current density, the growth of the unstable sound mode saturates after a
while. At this stage cold ions gather around the high density region since the negative
pressure arising from the electron convection term exceeds the pressure of the cold
ions. The discrete parallel electric field forms at the boundary of the high- and
low-density regions and prevents cold ions from going to the evacuated (unstable)
region. In the Io-Jupiter system, the parallel current density is nearly proportional to the
magnetic field intensity and the plasma density is roughly uniform along the field line
at the low altitude magnetosphere. It can be expected that the discrete parallel
electric field would form above the altitude where the parallel current density equals
the critical current density.
MOP2011-P0020
Poster (Contributed)
Planetary period oscillations in Saturn's magnetosphere: Evidence in
magnetic field phase data for rotational modulation of Saturn kilometric
radiation emissions
Andrews, D.J.[1], B. Cecconi [2], S.W. Cowley [1], M.K. Dougherty [3], L. Lamy [2], G.
Provan [1] and P. Zarka [2]
[1] Department of Physics and Astronomy, University of Leicester
[2] LESIA, Observatoire de Paris, Universite Paris Diderot, Meudon
[3] Blackett Laboratory, Imperial College
Initial Voyager observations of Saturn kilometric radiation (SKR) indicated that the
modulations in emission power near the ~11 hour planetary rotation period are
'strobe-like', varying with a phase independent of observer position, while subsequent
Cassini studies of related oscillations in the magnetospheric magnetic field and
plasma parameters have shown that these rotate around the planet with a period
close to the SKR period. However, analysis of magnetic oscillation data over the
interval 2004 -- 2010 reveals the presence of variable secular drifts between the
phases of the dominant southern-period magnetic oscillations and SKR modulations,
which become very marked after Cassini apoapsis moved for the first time into the
post-dusk sector in mid-2009.
Here we use a simple theoretical model to show that
such phase drifts arise if the SKR modulation phase also rotates around the auroral
oval, combined with a highly restricted view of the SKR sources by the spacecraft due
to the conical beaming of the emissions. 'Strobe-like' behavior then occurs in the
pre-dawn-to-noon sector where the spacecraft has a near-continuous view of the
most intense mid-morning SKR sources, in agreement with the Voyager findings, while
elsewhere the SKR modulation phase depends strongly on spacecraft LT, being in
approximate anti-phase with the mid-morning sources in the post-dusk sector.
Supporting evidence for this scenario is provided through an independent
determination of the variable rotation period of the southern magnetic field
perturbations throughout the 6 year interval.
MOP2011-P0051
Poster (Contributed)
Currents and Associated Electric Fields in Titan's Ionosphere
Ågren, K. [1], D.J. Andrews [2], A.J. Coates [3], S.W. Cowley [2], M.K. Dougherty [4],
N.J. Edberg [1], R. Modolo [5], G. Provan [2], J. Wahlund [1] and A. Wellbrock [3]
[1] Swedish Institute of Space Physics, Uppsala
[2] Department of Physics and Astronomy, University of Leicester
[3] Mullard Space Science Laboratory, University College
[4] Blacket Laboratory, Imperial College
[5] UVSQ/LATMOS, IPSL/CNRS INSU
In this study we use calculated conductivities at Titan in combination with Langmuir
probe (LP) and magnetometer (MAG) measurements by Cassini in order to examine
the cold plasma properties in the deep ionosphere of the moon.
By calculating the
curl of the magnetic field and adapt the conductivity computations to the results, we
infer currents and electric fields with direction and magnitude.
MOP2011-P0080
Poster (Contributed)
Investigation of Jovian Thermospheric Temperature by the Observation of
H2 and H3+ Auroral Emission
UNO, T. [1], T. Sakanoi [1], C. Tao [2] and Y. Kasaba [1]
[1] Geophysics, Tohoku
[2] ISAS, JAXA
Jupiter, the largest planet, has the strongest and largest magnetosphere in the solar
system. There have been many attempts to observe the Jovian thermospheric
temperature with varying degrees of success. Early spectroscopic studies (e.g., Kim et
al., 1990; Ballester et al., 1994) focused on the determination of the mean H 2 and H3+
temperatures or the vertical thermal structure in the northern and southern auroral
regions. From high spectral resolution 2 um imaging observation, Raynaud et al., 2004
showed that the spatial distribution of the emission from H 2 and H3+ aurora are
morphologically different. The origin of this morphological deference is still unknown. It
potentially suggests the difference of emission altitude or the difference of energy
injection to and the energy transfer between the neutral and plasma atmospheres.
We have studied this region by numerical simulations (e.g., Tao et al., 2009) and have
compared them with multiple wavelength observation data of infrared aurora (2-4
um) taken with a ground-based telescope. In addition to the emission distributions, we
focus on the temperature information to investigate neutral-ion coupling in the Jovian
upper atmosphere: How and where does the energy input occur into the neutral and
plasma upper atmospheres?
In Oct. 12 2010, simultaneous H2 and H3+ observations near 2.1 um took place using
the SUBARU/IRCS. The slit is set along rotational axis (vertical to the auroral main oval)
at northern/southern pole. In the polar region, H2 emission lines S1(0), S1 (1), and S1 (2) at
the wavelengths of 2.22, 2.12, 2.03 um and several H3+ emission lines are detected. The
wide spectral coverage and the high sensitivity of SUBARU/IRCS enable us the
rotational/vibrational temperature measurement from the simultaneous observation
of the distribution of emission lines. We will report the difference in the spatial
distributions of the emission and temperature of neutral and plasma atmosphere,
derived from the data of the observation.
MOP2011-P0083
Poster (Contributed)
The Roles of Dissociation and Velocity-Dependent Charge Exchange in
Saturn's Extended Neutral Clouds
Fleshman, B.L.[1,2], P.A. Delamere [2] and F. Bagenal [2]
[1] Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma
[2] Laboratory for Atmosphere and Space Physics, University of Colorado
The Enceladus plumes are directly responsible for the input of water-based neutrals in
orbit between 3 and 5 Rs from Saturn.
This material in turn indirectly feeds a larger
neutral cloud out to ~20 Rs by way of low-velocity charge exchange [Johnson et al.
2006], dissociation (by photons and electrons), and collisions between neutrals via
induced dipole interactions [Cassidy et al. 2010]. In this paper, we revisit the role of
charge exchange.
Charge exchange cross-sections depend on the reacting
species and their relative motion, particularly at low velocities, where most of the
relevant neutral products are created.
We test the influence of various
velocity-dependent charge exchange cross-sections, finding that the associated
oxygen cloud is the most extended, with the water and OH less spread out.
We
demonstrate that the contribution to the extended cloud from the Enceladus plume
itself is not significant compared to production from the global Enceladus torus (3-5 Rs).
We also test the sensitivity of the neutral clouds' source to the energy of dissociated
neutrals,
and
find
that
photo-dissociation
dominates
both
electron-impact
dissociation and charge exchange out to ~7 Rs, while impact dissociation remains as
important as charge exchange out to ~15 Rs. Compared to Cassidy et al. (2010), we
find molecular species have lower densities, but we find similar density of atomic
oxygen. These results are consistent with our model not including neutral-neutral
collisions.
Finally, we use these profiles of neutral material as the source for a
chemical calculation (where hot-electron flux and ion radial transport are free
parameters) to derive radial profiles of plasma composition, density and temperature
that we compare with Cassini observations.
MOP2011-P0098
Poster (Contributed)
High Resolution Spectrum Analysis of Jupiter's Lyman-alpha Bulge
Corbin, B.A.[1], J.T. Clarke [1] and L. Ben Jaffel [2]
[1] Center for Space Physics, Boston University
[2] IAP-CNRS-UPMC, Institut d'Astrophysique de Paris
High resolution spectra of Jupiter's Lyman-alpha bulge region taken from the Hubble
Space
Telescope
Imaging
Spectrograph
have
been
reanalyzed
to
better
characterize the hydrogen column density and the source of excess brightness in the
region. It was shown that at the bulge, there is a hot hydrogen emission feature in the
line profile below a cool hydrogen emission. This hot hydrogen layer was shown to be
moving at supersonic speed with respect to the cool layer in the direction of planet
rotation. Analysis of the anti-bulge region line profiles showed a similar atmospheric
layering, but the hot hydrogen was moving more slowly but still with supersonic speed
with respect to the cold layer. The spectra also show evidence of turbulence,
indicative that a Voigt spectral distribution is not sufficient for describing the spectral
width of the hot region. An optical depth analysis has shown that because of the
broad spectral profile, the excess brightness can be explained without requiring a
much higher column density of hydrogen in the bulge. This study supports the idea
that the bulge region is caused by an asymmetry in Jupiter's magnetosphere
combined with equatorial electrojets in the upper atmosphere.
MOP2011-P0131
Poster (Contributed)
Upper limits on Enceladus' airglow emission
Zastrow, M. [1] and J.T. Clarke [1]
[1] Boston University, Center for Space Physics
We report upper limits on airglow emissions from Enceladus' atmosphere in far
ultraviolet observations from the Cosmic Origins Spectrograph (COS) on the Hubble
Space Telescope (HST), including C, N, and O. We find these upper limits to be low, on
the order of tens to hundreds of Rayleighs. Enceladus is thought to be the source of
most of Enceladus' magnetospheric plasma. This lack of airglow may relate to the
interaction of the atmosphere with the magnetospheric plasma.
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