Mass Transport: To the Plasma Sheet – and Beyond!
Terry Onsager, Joe Borovsky, Joachim Birn, and many friends
• Transport into the Plasma Sheet
• Transport within the Plasma Sheet
• Transport from the Plasma Sheet into the
Inner Magnetosphere
Where does the plasma sheet come from, and why does it
have the properties it has?
Transport – is a topic proposed for a new GEM campaign
We propose that within this campaign, a working group be devoted to
modeling mass transport into, within, and from the plasma sheet.
Modeling the plasma sheet presents an opportunity to test our
knowledge of processes occurring throughout the magnetosphere and
ionosphere, and it is an obligation in order to fulfill GEM’s goals.
• Plasma Sheet has a dominant role in magnetospheric dynamics
• It is a relatively slowly varying integrator of numerous source, loss, and
transport processes.
• It provides an opportunity to test our understanding magnetosheath,
boundary layer, ionospheric, and magnetotail processes.
• It is a conduit for mass into the inner magnetosphere.
• Global magnetospheric models are running and increasingly relied on.
The plasma sheet is a critical element of these models, and it valuable
location to test our understanding and to and guide further research.
Magnetopause and Boundary Layers for Southward IMF
Mantle
Lobe
Cusp
Polar
Rain
LLBL
Cusp
Plasma Sheet
Polar
Rain
Lobe
Mantle
Magnetopause
Convection Paths for IMF Bz < 0
Lockwood, 1995
• Closed magnetic field convects outward to the magnetopause and interconnects
with magnetosheath field.
• Magnetospheric, ionospheric, and magnetosheath plasma flows freely into and
out of the magetosphere across the open regions of the magnetopause.
• Open field lines convect over the poles and into the magnetotail.
Pilipp and Morfill, 1978
Particle with low parallel speed
Particle with high parallel speed
• Magnetosheath plasma continuously crosses the magnetopause boundary and
convects toward the plasma sheet as it flows tailward.
• The distribution of parallel velocities and the ExB drift speed control the plasma
content on field lines that reconnect in the tail.
• Plasma heating occurs in the current sheet on the newly closed field lines.
• Near-Earth reconnection can trap solar wind plasma in the near-Earth plasma
sheet, even though convection in the distant plasma sheet may be tailward.
Observed at FAST
Alfven Waves
Ion Outflow
Electron Precipitation
(Magnetosheath)
Poynting Flux
ELF/VLF Waves
(Heating)
Inferred
Ion Upwelling
T. Abe
Ion Scale Height
Increase
Joule Dissipation
Causal
Bob Strangeway
Electron Scale Height
Increased Ambipolar Field
Electron Heating/Ionization
Possible Causal
Correlated
Various electron, ion, and
electrodynamic process are
responsible for heating and
accelerating ionospheric plasma.
Transport of Ionospheric Plasma to the Magnetotail
• Thermal cusp H+ (15
eV) are lost downtail
• Thermal O+ from the
cusp and H+ from the
nightside auroral zone
are energized in the
plasma sheet
• Thermal O+ from the
nightside auroral zone
receive little energy
• Dayside auroral
outflow (500 eV) is
lost downtail.
• Most H+ are lost
downtail.
• Nightside auroral O+
outflow is energized
in the plasma sheet.
Delcourt et al., 1990; 1993
H+ and O+ outflow rates
(0.01-17 keV) integrated
over all MLT and all
latitudes about 56º
Yau et al., 1988
• H+ outflow rate increases by about a factor of 4 from Kp = 0 to 6.
• O+ outflow rate increases by about a factor of 20 from Kp = 0 to 6.
• H+ outflow rate is independent of solar activity level (F10.7).
• O+ outflow rate increases with increasing solar activity.
• Flux of ionospheric ions is strongly
correlated with variation in solar
wind dynamic pressure
• Flux of ionospheric ions is not
strongly correlated with IMF Bz
Moore et al., 1999; Elliott et al., 2001
Convection Paths for IMF Bz > 0
Lockwood, 1995
• High latitude lobe and plasma sheet field lines convect to the magnetopause and
reconnection with magnetosheath field lines poleward of the cusp.
• Magnetopause crossing point of the new lobe field line moves downtail.
• New lobe field line eventually returns to the dayside magnetopause and continues
the lobe-cell circulation.
• No contribution to filling the plasma sheet results.
Capture of Magnetosheath Plasma for IMF Bz > 0
• If reconnection occurs at high latitudes,
new closed field lines will be formed
with a mixture of magnetosheath and
magnetospheric plasma.
• Reconnection has been shown to occur
first in one hemisphere and then the
other, not simultaneously in the two
hemispheres.
• Reconnection occurs over a large localtime range on the magnetopause, even
though the ionospheric footprint could be
small.
Song and Russell, 1992
Convection Paths for IMF Bz > 0
Lockwood, 1995
• High latitude lobe and plasma sheet field lines convect to the magnetopause and
reconnection with magnetosheath field lines poleward of the cusp in both
hemispheres.
• The subsequent convection of the new closed flux tube into the magnetotail is not
well known, but may be an important source of the plasma sheet.
MHD Simulations of Plasma Sheet Filling with IMF Bz > 0
Closed Magnetic
Topology
Raeder et al, 1995
80 minutes after northward IMF turning
225 minutes after northward IMF turning
• New closed field lines form through high-latitude magnetopause reconnection.
• Boundary layer plasma convects tailward and toward the tail center.
• Open tail flux becomes narrowly confined to the center of the tail as the
boundary layer expands.
Geotail Observations of Plasma Sheet Density and Temperature
Terasawa et al., 1997
• Northward IMF: High density and low temperature
• Southward IMF: Low density and high temperature
Wind Observations of Plasma Sheet Density
Versus IMF Theta Angle
Cold, Dense Plasma Sheet:
Ne > 0.7; Te < 200 eV
• Cold, dense plasma sheet forms after
prolonged northward IMF.
• Cold, dense plasma sheet is observed on
the dawn and dusk flanks.
Oieroset et al., 2003
Geotail observed the
flank LLBL ~13-15 RE
downtail over ~ 5 hours
with steady IMF Bz > 0.
Fairfield et al., 2000; Otto and Fairfield, 2000
• Comparison of plasma and field fluctuations observed and from 2-D MHD
simulation results showed strong agreement.
• Vortices require several minutes to form. They form at X ~ -15 RE, and have a
size of about 2 RE.
• Reconnection within the vortices is responsible for mass transport.
• Recent article argues against mass transport by this process [Stenuit et al., 2002].
• Geotail and Wind crossed the
magnetotail at a downtail
distance of about 15 - 20 RE.
• Geotail led Wind by about 5 RE
in the cross-tail direction.
• Geotail and Wind simulaneously
measured the increase in plasma
sheet density and decrease in
temperature as the IMF became
northward.
• This observation may indicate
that the change in plasma sheet
is moving down the tail, rather
than across the tail from the
flanks.
Oieroset et al., 2003
8 hr
Borovsky et al., 1998
Fuselier et al., 1999
Modeled Storm Magnitude Depends on Plasma Sheet Density
Nps fixed at pre-storm value
Nps variation in RAM
as observed by LANL GEO
Kozyra et al., 1998
Modeled Storm Magnitude Depends on Plasma Sheet Temperature
Ebihara and Ejiri, 2000
• Radiation belt electrons exhibit abrupt enhancements and loss driven by the solar
wind and magnetospheric conditions.
• Radiation belt loss occurs with the onset of geomagnetic activity following a
period of prolonged quiet.
• Loss initiates with strong distortion of the inner magnetospheric magnetic field,
and may be due to the sunward convection of a cold, dense plasma sheet.
Janet Green
M = 2100 MeV/G
3x10-9
Geosynchronous
Orbit
Hilmer et al., 2000
ISEE 1
11 RE Downtail from Earth
Williams et al., 1990
• Plasma sheet electron and ion
heating was associated with
current sheet disruption and field
dipolarization.
• Phase space density in the nearEarth plasma sheet is comparable
to phase space density at
geosynchronous orbit.
• Plasma Sheet:
M  2800 MeV / G
j
f me3  2 2 1.66 10 10 s 3 km6
pc


 3 10 9 s 3 km6
• Geosynchronous Orbit:
M  2100 MeV / G
f me3  3 10 9  10 8 s 3 km6
Summary
• The plasma sheet is the place through which mass flows: from the solar wind and
the ionosphere, then into the inner magnetosphere and out to the solar wind.
• Plasma transport and heating are influenced by the IMF, with transport time scales
typically longer than time scales of IMF variability.
• Southward IMF leads to a hot and tenuous plasma sheet.
• Northward IMF leads to a cold and dense plasma sheet.
• Both solar wind and ionospheric plasma contribute importantly to the plasma sheet,
yet the variability in the relative fraction is not known.
• Understanding transport from the ionosphere and from the magnetosheath is critical
to understanding the plasma sheet.
• Understanding the plasma sheet it critical to being able to understand and model the
inner magnetosphere.
• GEM should take the challenge to model geospace transport, with modeling the
plasma sheet as one specific goal to demonstrate our understanding.