Relation between joule heating and thermospheric neutral density during geomagnetic storms

It is well-known that the thermospheric neutral density is influenced by the variations in Joule heating during geomagnetic disturbances. However, the details of the timing and location of the thermospheric response and their relationship with the thermospheric energy deposition are still not completely understood and are active research subjects. In this study, the correlation between Joule heating (JH)and thermospheric neutral density was investigated for six geomagnetic storms and simple relations between JH and thermospheric neutral density were constructed using two physics-based ionosphere-thermosphere models. Joule heating was obtained from Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM)and Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) models, while Challenging Minisatellite Payload (CHAMP)observations were used for the thermospheric neutral density. The correlation coefficients for JH and neutral density were calculated using three different data sets, which contained 1)data from all six geomagnetic storms, 2)data from individual events, and 3)storm-time integrated data. It is found that the observed global thermospheric neutral density response in CHAMP shows a delay from one to four hours with respect to the variations in the model JH. CTIPe shows the best correlations with CHAMP neutral density for the first two data sets: Four of the six events and when all geomagnetic storms' data were used. On the other hand, TIEGCM shows higher correlation coefficients and less errors in terms of root sum square error for the storm-time integrated values.