Authors: J.M. Forbes, S. Nerem, X. Zhang, E. Sutton; G. Lu, A.D. Richmond,
R.G. Roble; S. Bruinsma
Affiliation: University of Colorado; National Center for Atmospheric Research,
High Altitude Observatory; Centre National d’Etudes Spatiales, France
The accelerometer on the CHAMP satellite measures atmospheric drag between about 390 and 430 km, from which the total mass density in the in-track direction, and under some conditions, winds in the cross-track direction, can be inferred. In this work, the CHAMP densities (normalized to a constant altitude of 410 km) are utilized to delineate the evolution of the thermospheric response to varying geomagnetic activity, with approximately 1.5-hour time resolution, on both day and night sides of the Earth and extending nearly pole to pole. Several intervals containing large geomagnetic disturbances are examined here, including the 15-24 April, 2002, Storm Study period, and the large storms of October/November, 2003. Comparisons are made with the MSISE90 empirical model, and with the NCAR Thermosphere-Ionosphere-Electrodynamics Model (TIEGCM) for the same solar-geophysical conditions. Evidence for the propagation of traveling atmospheric disturbances (TADs) from the auroral/polar region, to the equator, and into the opposite hemisphere, with phase speeds of 800 m/sec, are revealed. Smaller-scale waves are also present in the data at high latitudes, but do not propagate far from the auroral/polar source. In addition, wave activity at all scales is suppressed during the day compared to night, presumably due to greater dissipation by ion drag. These observed characteristics are in accord with theoretical expectations. If time permits, the first comparisons between CHAMP and GRACE accelerometer measurements will be shown.