Thermospheric density variation and its response to Joule heating during geomagnetic storms

Thermospheric density is essential for the calculation of atmospheric drag, which is the main cause of the orbit decay for low-Earth-orbit (LEO) satellites. During geomagnetic storms, the Joule heating has a strong impact on neutral mass density. In this work, we statistically investigate 265 geomagnetic storms to explore the response of thermospheric density to Joule heating from 2002 to 2008. We obtain the density enhancements from Challenging Minisatellite Payload (CHAMP) and the Gravity Recovery and Climate Experiment (GRACE) satellites, and we also calculate Joule heating from the Defense Meteorological Satellite Program (DMSP) spacecraft and the Weimer electric potential model. The results show that the thermospheric density delays Joule heating during geomagnetic storms. The time lag is about 0-2 hrs during weak and moderate storms, while it is 3-5 hrs for intense storms. In addition, Joule heating can affect the density enhancement at higher latitude regions. The latitudinal difference between thermospheric density and Joule heating is about 0°-10° during weak and moderate geomagnetic storms, while it increases to 10°-15° for intense storms. Besides, we use the temporal relationship of thermospheric density with geomagnetic activity indices and Joule heating as calibration for the NRLMSISE-00 model during geomagnetic storms. The calibrated NRLMSISE-00 model results can better simulate the storm-time thermospheric density, with the Mean Relative Error (MRE) between observation and model decreasing from 40% to 10%.