Globally- and hemispherically-integrated Joule heating rates during the 17 March 2015 geomagnetic storm, according to physics-based and empirical models

Abstract

Joule heating is a primary energy dissipation mechanism of the solar wind in the Earth’s upper atmosphere. However there are large discrepancies in the computation of Joule heating between models. In this study, we perform a comparison of the Joule heating rates between two of the most commonly used physics-based Global Circulation Models (GCM) of the Earth’s upper atmosphere: the Global Ionosphere/Thermosphere Model (GITM) and the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). Both GCMs are externally driven by models that provide the specification of high-latitude electric fields as well as auroral precipitation. In this study, each model is driven by two different specifications of high-latitude electric fields, namely the Weimer 2005 and the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) models. Several empirical formulations are also commonly used to estimate Joule heating rates as a function of various indices of solar and geomagnetic activity; a further comparison is performed between these empirical formulations and the GCMs. We find that the empirical formulations generally give lower estimates of Joule heating rates compared to both GCMs, GITM and TIE-GCM. We also find that TIEGCM provides lower estimates of the heating rates compared to GITM when the Weimer 2005 model is used as driver, whereas TIE-GCM and GITM give rather similar estimates when the AMIE model is used, with TIE-GCM occasionally giving higher estimates. Estimates of Joule heating rates separately for the two hemispheres indicate that higher Joule heating rates are observed in the Southern Hemisphere when the Weimer model is used, both in GITM and TIE-GCM. However, when the AMIE method is used, higher Joule heating rates are calculated for the Northern Hemisphere. The comparisons between the two Global Circulation models and the empirical models are discussed.