Storm-time energy budget in the high latitude lower thermosphere–ionosphere: quantification of energy exchange and comparison of different drivers in TIE-GCM

Abstract. The energy flow and energy balance in the Lower Thermosphere–Ionosphere (LTI) is governed by a number of processes that are driven by interactions between ions, neutrals and electrons. Even though these processes are well understood theoretically, and even though the framework to implement these processes exists in current global circulation models, the energy estimates for the different processes show large discrepancies between models, in large part because of limitations in available data sets. In this study, we explore numerically the energy inputs and energy transfer between ions, neutrals and electrons during the 2015 St. Patrick's day geomagnetic super-storm. We use NCAR's Thermosphere Ionosphere Electrodynamics General Circulation Model, version 2.0 (TIE-GCM 2.0) for estimating energy sources and sinks, energy transfer rates and the energy partitioning between species. Two independent TIE-GCM runs were executed: the first one used the Weimer 2005 empirical model, and the second used the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) data assimilative technique. The resulting energy budget and the corresponding partitioning of energy between species are inter-compared between the two runs, before and at the peak of the storm. The energy budget is investigated individually for neutrals, ions and electrons, as different heating and cooling mechanisms are associated with each species. Discrepancies between the model runs are discussed and the way forward to close the gaps in present knowledge is highlighted.