Statistical analysis of thermospheric density changes seen by TIEGCM and CHAMP data during major geomagnetic storms

The spatial distribution of the thermospheric density would change greatly due to the particle precipitation during geomagnetic storms. These changes in thermospheric density cause the increases of air drag on low altitudes satellites, which will impact on the orbit and attitude of the satellites. Therefore, studies on the characteristics of the storm-time thermospheric density perturbation and the accuracy of thermospheric models are of great importance for both research and application meaning. In this article, the thermospheric densities at 410 km are simulated by the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) during 39 major geomagnetic storms (Dst<-100 nT) from 2001-2005, and compared with the densities observed by the CHAMP satellite. The deviations between TIEGCM and CHAMP are studied with different latitudes, sunlight conditions and geomagnetic indices, in order to examine the model accuracy of forecast. The statistical results show that, (1) the model results have a good agreement with the observational data during geomagnetic storms.However, some deviations do exist. (2) The storm-time thermospheric densities at 410 km have fine correlationship with the SYM-H index, and vary with latitudes, sunlight conditions, and geomagnetic indices. The differences of density changes between dayside and nightside are smaller than those of absolute values. The densities calculated by TIEGCM show the similar response to the SYM-H index, except for the smaller values. (3) The TIEGCM underestimates the magnitude of the density perturbation during geomagnetic storms, especially for those at high geomagnetic active levels. The deviations of modeled densities from the observed densities in the high latitude region are larger than those in the lower latitude region. They are also bigger on the dayside than those on the nightside. The deviations increase with the Dst index absolute value until the Dst reaches -150 nT. The deviations show little relativity with the SYM-H index. The statistical results have limitations due to the limited sample number, local time distribution and period in solar circle of the observation data.