On the relationship between thermosphere density and solar wind parameters during intense geomagnetic storms

Total mass density measurements at 72 degrees S, 0 degrees, and 72 degrees N latitude from the CHAMP satellite near 400 km altitude are used to provide a quantitative assessment of the relationship between solar wind energy input and density variations during intense (Dst <= -100 nT) geomagnetic storms that occurred between August 2001 and December 2006. Correlations between the thermosphere density variations and various solar wind parameters and coupling functions representing the energy input into the thermosphere reveal significantly different characteristics during different geomagnetic storms. Statistical analysis shows that, out of the chosen solar wind parameters including coupling functions, the Borovsky parameter correlates best with the global scale density variations. The correlations at the equator are significantly higher than those at high latitudes. Moreover, the correlations on the dayside are almost the same as those on the nightside at 72 degrees S and 0 degrees latitude, whereas the correlation on the nightside is slightly higher than that on the dayside at 72 degrees N latitude. These results indicate that it might be possible to use solar wind measurements to improve predictions of thermosphere density perturbations and the resulting changes in satellite drag.