Anomalous Behavior of the Thermosphere During the Solar Minimum

Details Anomalous Behavior of the Thermosphere During the Solar Minimum Anomalous Behavior of the Thermosphere During the Solar Minimum

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa22a..04b&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SA22A-04

Physics

[0355] Atmospheric Composition And Structure / Thermosphere: Composition And Chemistry, [0358] Atmospheric Composition And Structure / Thermosphere: Energy Deposition

Scientific paper

Accelerometers on the CHAMP and GRACE satellites have made it possible to accumulate near-continuous and simultaneous records of thermosphere density between about 320 and 490 km since mid-2002. CHAMP and GRACE are in near-polar and quasi-circular orbits, sampling 24 hrs local time approximately every 4 and 5 months, respectively. These capabilities offer unique opportunities to study temporal and latitudinal responses of the thermosphere to geomagnetic disturbances as well as tides. Due to the different precession rates of the orbits, the local times sampled by CHAMP and GRACE are not in general the same. However, there have been four instances when the orbital planes were co-planar (same local times), and the last of these occurred on 17 December 2008, under conditions representative of the recent deep solar minimum. During this time CHAMP and GRACE provide near pole-to-pole total mass density measurements at local times of 8.3 and 20.3 hr at altitudes of 332 and 476 km, respectively. The latitudinal structure of the observed densities is significantly different at the two altitudes. This is most probably due to a much higher than predicted presence of Helium at the GRACE altitude, which is indirectly visible in the total mass densities in the form of a large winter bulge. NRLMSIS00 predicts similar behavior, but for an altitude 100 km higher, and it overestimates the observed densities by 25-30% on average. In addition, both CHAMP and GRACE reveal longitudinal structures, although considerably different, with 2 to 3 maxima that we interpret as non-migrating tides from the lower atmosphere. These density perturbations are unusually large, with amplitudes typically of order +/- 10 to +/- 25 % about mean density levels.

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