Ionospheric electron temperature and density during geomagnetic storms: Comparison of DE 2 and GITM

The ionosphere - thermosphere (IT) system is known to exhibit several scales of variability in both spatial and temporal domains owing to its dynamic coupling with the magnetosphere and the lower atmosphere. During geomagnetic storms, there is a complex interplay of various phenomena in this region like Joule heating, thermal expansion, consequent composition changes in the equatorward wind which can lead to the upliftment of the F layer. Simultaneously, prompt penetration electric field instantaneously modifies the ExB drift leading to anomalous density gradients over a range of latitudes. Thus, the dramatic changes observed during storm time are controlled by several drivers making the forecast of this region extremely challenging. In the present study, in situ measurements of electron temperature and density obtained from the Langmuir Probe on board DE2 are compared with the GITM simulations to study major storms that occurred during the peak activity level of solar cycle 21. This study is an attempt to quantify the different storm-time plasma heat sources to explain the observed variability in the heating pattern along latitudes. This redistribution also exhibits hemispheric asymmetry in the electron temperature and density, discerned to have a seasonal pattern, as a resultant of several factors including differential EUV heating, conductivity changes and the transport mechanisms at play, which is unique for every storm. GITM simulations offer an insight into the physical processes that govern the state of the IT during storm time.