Jeffrey M. Forbes1, Eelco Doornbos2, Mark Conde3,
Sean L. Bruinsma4, Gang Lu5, Daniel Ober6
University of Colorado1; Delft University of Technology2; University of Alaska3;
Centre National d’Etudes Spatiales4; National Center for Atmospheric
Research5; Air Force Research Laboratory6
How does the magnetic field mediate the interaction between the neutral
atmosphere and ionosphere?
What have we learned from recent missions?
What will Swarm contribute?
1
Thermosphere and Ionosphere Densities
2
CHAMP neutral densities, 2005
• The highly variable IT system is relevant to satellite orbit and reentry
prediction, and to the operation of communications and navigation
systems.
• External drivers of the IT are solar EUV flux, solar wind energy reprocessed
by the magnetosphere, and meteorological disturbances originating in the
lower atmosphere.
• Interactions between the thermosphere and ionosphere, mediated by
Earth’s magnetic field, translate the above drivers into IT “space weather”.
• Swarm, combined with other key assets (see later slides), will enable
measurement of the IT system response to various drivers.
3
The Ionosphere-Thermosphere
(IT) System
Magnetospheric
Coupling
B
800 km
B
E
Energetic
Particles
E
Wind Dynamo
Polar/Auroral
Dynamics
Mass Transport
Joule Heating
Wave
Generation
90 km
IT System
Solar Heating
CO2 Cooling
Topographic
Generation
of Gravity
Waves
Turbulence
NO
O3
solar-driven tides
Planetary Waves
0 km
Pole
CO2
CH4
Convective
Generation
of Gravity
Waves & Tides
H2O
Equator
4
• Statistical relationships developed between interplanetary magnetic field
(IMF) configuration and polar region neutral densities, winds, and plasma
drifts, with significant hemispheric asymmetries.
• Lower atmosphere variability drives significant IT variability through the
vertical propagation of waves, both directly and indirectly through the
dynamo generation of electric fields.
• High-speed solar wind streams emanating from coronal holes impose
periodicities on the IT system at subharmonics of the solar rotation period
(27, 13.5, 9, 6.7 days).
• Regional and local structures at low latitudes discovered that likely have
their origins in plasma-neutral coupling.
5
Classic
Geoeffective
Solar WindMagnetosphere
Coupling
IMF Bz < 0
1
2
3
4
6
8
5
7
magnetic
merging
IMF
Bz < 0
Forster et al., 2011
6
opposite in
direction to
electrons, or feet
of field lines
E-region Hall currents
F-region plasma drifts
7
co-vary over long time scales
but not short time scales
On Swarm, this will be possible all
the time, due to the coincident
measurement of plasma drifts and
neutral winds.
recovery depends
on NO cooling
In addition, the neutral and plasma
densities, which determine the
time scale of the neutral wind
response, will also be measured
8
Cusp or sidelobe reconnection occurs
when Bz > 0 and By >> 0
Maezawa
(1976)
First principles models reveal physical processes
[Deng et al., 2011; Crowley et al., 2010]
Significant energy enters dayside
thermosphere without enhancements in
traditional magnetic indices [Knipp et
al., 2011; Li et al., 2011]
S = ( E ´ d BDMSP ) / m0
FACs accompany this reconnection
process.
Closure of the FACs results in Joule
heating and density increases
CHAMP
density
enhancement
FACs
Luhr et al., 2004
Forster et al., 2011
9
S. Hemis.
N. Hemis.
Statistical distribution of
cusp density anomalies
during 2005 [Rentz and
Lühr, 2008].
Note the strong
hemispheric differences.
Statistical distributions
of neutral wind vorticity
for By < 0 (left) and By >
0 (right) over S. polar
region [Förster et al.,
2011]
10
w- >> nen
w+ >> nin
Ñ ´B =
J
m0
F-Region
e-
Ñ× J =0
J = sE = s [-ÑF + Vn ´ B]
O+
V+,-
equipotential
line
Global electrostatic
field set up by
dynamo action
e-
w- >> nen
w+ ~ n in
B
E´B
=
B2
Vn
O2+, NO+
Tidal structures at 110 km: An upper atmosphere
signature of wave-4 land-sea differences
E-Region
11
CHAMP revealed the longitude structures of tidal dynamo-induced Sq currents,
electrojet currents and ionospheric plasma densities, but not the electric fields
that tie all of these together
CHAMP Sq currents
Pedatella et al., 2008
CHAMP electron densities
July, 2004
Pedatella et al., 2011
Electrojet currents
Alken & Maus
Swarm will also measure the
electric fields globally 12
CHAMP & GRACE also revealed that the tides propagate to orbital altitudes
Longitude structures of exosphere temperature &
density tides attributable to troposphere forcing
DE3 Zonal winds over the equator, 400 km
CHAMP,
Häusler & Lühr
SABER & theory,
Oberheide
DE3
DE2
CHAMP-DE3 @ 390 km
SABER extrapolated by theory 100  390 km
Propagation of tides into
the thermosphere exhibit
a solar cycle dependence
due to the way that
molecular diffusion
dissipates the tides
13
Ground-based measurements
of winds at satellite altitudes
available from a number of
locations
Ground-based measurements
capture high spatio-temporal
variability
Valuable for both validation and
scientific studies.
14
Apr 5, 2010
First-Principles models
•
Place the measurements in
perspective (note that the satellite
measurements only provide the
cross-track wind component)
•
Provide the context to better
understand plasma-neutral
interactions
15
ICON’s science objectives are
to understand:
• the sources of strong
ionospheric variability;
• the transfer of energy and
momentum from our
atmosphere into space; and
• how solar wind and
magnetospheric effects modify
the internally-driven
atmosphere-space system.
ICON will measure:
Temperatures, Winds, Plasma
drifts, Neutral composition
Michelson Interferometer
EUV Imager
Ion Velocity Meter
UV Imager
16
First-Principles & Assimilative
Models
Iridium/AMPERE
ACE
GOCE
Ground-based Observations
17
• Swarm A/B will separate from Swarm C (530 km) in altitude and local time (460 km
to 300 km after 4 years; > 3 hours after 18 months)
• Swarm electric and magnetic field measurements
will enable Poynting Flux to be determined
S = ( E ´ d B) / m0
• Coincident plasma drift, neutral wind, and neutral and plasma densities will be
made.
• High inclination, so all latitudes are covered.
• No neutral and plasma composition measurements
• Restricted local time coverage
• No in-track wind measurements.
• No measurements of upward-propagating waves in the lower IT region (100-150 km)
18
• Swarm+ will enable more of a “system-level” perspective.
• Swarm+ measurements will not fully define the IT system, but it will significantly
constrain the system.
• Defining the system will involve assimilation of Swarm+ data into first principles
models to guide the solutions of these models.
 How are energy and momentum transferred from the plasma to neutrals in the polar
regions over various temporal scales?
• How is this exchange controlled by the interplanetary magnetic field (IMF)?
• What are the hemispheric differences imposed by Earth’s B-field?
 How do high-latitude energy and momentum inputs influence middle and low latitudes?
• How does the magnetic field mediate this transfer and the plasma neutral
interactions that are involved?
 What aspects of IT variability in electric fields, currents, neutral winds, neutral and
plasma densities are attributable to influences from the lower atmosphere?
• How does the magnetic field mediate the transfer of momentum and energy
between the atmosphere and ionosphere?
19