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 the primary solar wind energy dissipation mechanism in the Earth's upper atmosphere, however its estimates vary greatly between models, due to a lack of co-located, co-temporal measurements of all the parameters needed for its estimation. In this study, hemispherically- and globally-integrated Joule heating rates are estimated during the major geomagnetic storm of 17 March 2015, using two of the most commonly used physics-based Global Circulation Models (GCM) of the Earth's upper atmosphere: These are the Global Ionosphere/ Thermosphere Model (GITM) and the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). Both are externally driven by models that provide the specification of high-latitude electric fields as well as auroral particle precipitation. A comparison of the evolution of the globally-integrated Joule heating rates is performed between the two physics-based models, TIEGCM and GITM, each 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 provide estimates of Joule heating based on solar and geomagnetic activity indices; a further comparison is performed between these empirical formulations and the GCMs. It is found that all empirical formulations underestimate Joule heating rates compared to GITM and TIEGCM, whereas TIEGCM calculates lower heating rates compared to GITM, both when Weimer 2005 and AMIE models are used as drivers. By calculating the heating rates in the northern and southern hemispheres it is found that in GITM and TIEGCM higher Joule heating rates are observed in the southern hemisphere, when the Weimer model is used. These discrepancies disappear when the AMIE method is used. In that case higher Joule heating rates are calculated for the northern hemisphere. The differences and similarities between the two GCMs and the empirical models are discussed.