Atmospheric Neutral Density and Solar Indices Workshop

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Neutral Density and Wind Responses to the Severe
2003 Geomagnetic Storms from CHAMP GRACE
Accelerometer Data
J. M. Forbes, E. K. Sutton R. S.
Nerem Department of Aerospace Engineering
Sciences, University of Colorado, Boulder,
Colorado, USA
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CHAMP is in a 1320/0120 LT orbit during the
Super Storms
CHAMP cross-track wind measurement much less
susceptible to contamination by errors in
radiation pressure modeling.
Local time precession rate of CHAMP is about 24
hours/133 days The GRACE satellites are in a
1600/0400 LT orbit during the Super Storms
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Thermosphere Density Response to the
October/November 2003 Storms from CHAMP
Accelerometer Measurements
200 -300
200
EUV Flare 50
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Thermosphere Density Response to the October 28,
2003 EUV Flare from CHAMP GRACE Accelerometer
Measurements
50 increase
50 increase
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Cross-Track Winds are Derived from the
Cross-Track Accelerometer on CHAMP
Density from in-track accelerometer
Satellite velocity relative to a co-rotating
atmosphere
Sine (angle) between the cross-track axis and
geographic east for CHAMP during October 27 -
November 2, 2003
Wind relative to co-rotating atmosphere
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Cross-Track DMSP Ion Velocities and CHAMP Neutral
Winds
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Cross-Track CHAMP and HWM-93 Neutral Winds
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Daytime (LST 1320) Zonal Winds at the Equator
Westward winds during quiet period
Westward intensification during disturbed period
Note longitude also changing _at_ 360/day
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Nighttime (LST 0120) Zonal Winds at the Equator
HWM93 50 to 100 m/s during quiet period
CHAMP 0 to -50 m/s during quiet period
CHAMP strong westward intensification during
disturbed periods
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TEC Measurements Suggest a Possible Combination
of Electrodynamic, Dynamical and Chemical
Effects at the Equator
Suggests enhanced eastward electric field,
vertical drifts, and vertical redistribution of
equatorial plasma -- reduction or increase in
east-west drag at 410 km? TEC asymmetry possibly
imply northward wind?
Equatorial plasma depletion reduces ion
drag? Reduction in O/N2 ratio or transport
effect?
Credit International GPS Service -
http//igscb.jpl.nasa.gov
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posible radiation pressure modeling errors, which
maximize around dusk/dawn
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GRACE-A and GRACE-B Cross-Track Winds
Differences due to inaccuracies in estimated
cross-track biases
Earth shadowing effects not fully removed
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HWM-93 and GRACE-B Cross-Track Winds
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SUMMARY AND CONCLUSIONS
CHAMP GRACE Density Perturbations

• 200-300 increases with magnetic activity,
  asymmetric
• about equator -- larger than symmetric
  NRLmsise00
• 50 increase with solar EUV flare

CHAMP Zonal Winds at the Equator

• Daytime -100 ms-1 --gt -200 to -300 ms-1 with
  magnetic activity
• Nighttime 0 ms-1 --gt -200-250 ms-1 with
  magnetic activity
• Combined effects of zonal electric field and ion
  drag likely
• Best interpreted with TIEGCM-like model

GRACE Developing a thermosphere wind database

• improve GRACE-A/GRACE-B bias estimates
• improve shadow model radiation pressure model

• Many future possible synergies with C/NOFS
• CHAMP GRACE WINDS constrain first-principles
  models
• -----gt more realistic neutral densities