Impact of Soft Electron Precipition on the Thermospheric Neutral Mass Density During Geomagnetic Storms: GITM Simulations

In this study, the impact of improving soft (0.1-1 keV) electron precipitation on the F-region neutral mass density has been evaluated using the Global Ionosphere Thermosphere Model (GITM). Two types of electron energy spectra having the same total energy flux and average energy but different spectral shapes have been used to specify the electron precipitation in GITM. One is the Maxwellian spectrum and the other is from an empirical model, Auroral Spectrum and High-Latitude Electric field variabilitY (ASHLEY), which provides stronger (up to 2-3 orders of magnitude) soft electron precipitations than the Maxwellian spectrum. Data-model comparisons indicate that the storm-time orbital averaged neutral density can be increased by 10%-40% and is more consistent with the observation if the non-Maxwellian ASHLEY spectrum is used. This study reveals the importance of accurate soft electron precipitation specifications in the whole auroral zone to improving the F-region neutral mass density estimations. Plain Language Summary During geomagnetically active periods (i.e., geomagnetic storms), the neutral density above 150 km (i.e., in the F-region) undergoes substantial (can exceed 100%) enhancements. The denser atmosphere prevents satellites flying in their intended orbits and could cause the satellite to reenter the atmosphere or collide with other satellites/space debris, leading to the deconstruction of satellites. Hence, it is essential to accurately predict the storm-time neutral density variations to improve satellite operation and reduce satellite collision risk. Numerical models have been widely utilized for such purpose but discrepancies between simulations and observations have been identified. This discrepancy could be caused by inaccurate specifications of the electron precipitation in the auroral zone, especially the low-energy (0.1-1 keV) electron precipitation. In this study, a new electron precipitation model which improves the specification of low-energy electron precipitations has been coupled into a numerical model, Global Ionosphere Thermosphere Model. Data-model comparisons across a wide range of geomagnetic storms show that the neutral density averaged over the orbit can be increased by 10%-40% and is more consistent with the satellite observation if more accurate low-energy electron precipitation is included. This study highlights the necessity of better specifying low-energy electron precipitations to the prediction of F-region neutral density.