Comparison of global Joule heating estimates in GITM, TIE-GCM and
empirical formulations during St. Patrick's Day 2015 geomagnetic storm
Abstract
It is well known that the primary solar wind energy dissipation
mechanism in the Earth’s upper atmosphere is Joule heating. Two of the
most commonly used physics-based Global Circulation Models (GCM) of the
Earth’s upper atmosphere are the Global Ionosphere/ Thermosphere Model
(GITM) and the Thermosphere-Ionosphere-Electrodynamics General
Circulation Model (TIE-GCM). At the same time, a number of empirical
formulations have been derived to provide estimates of Joule heating
rates based on indices of solar and geomagnetic activity. In this paper,
a comparison of the evolution of the globally-integrated Joule heating
rates between the two GCMs and various empirical formulations is
performed during the solar storm of 17 March 2015. It is found that all
empirical formulations on average underestimate Joule heating rates
compared to both GITM and TIE-GCM, whereas TIE-GCM calculates lower
heating rates compared to GITM. It is also found that Joule heating is
primarily correlated with the auroral electrojet in GITM, whereas Joule
heating in TIE-GCM is correlated better with the Dst index and with
prolonged southward turnings of the Interplanetary Magnetic Field
component, Bz. By calculating the heating rates separately in the
northern and southern hemispheres it is found that in GITM higher Joule
heating rates are observed in the northern hemisphere, whereas in
TIE-GCM higher Joule heating rates are observed in the southern
hemisphere. The differences and similarities between the two global
circulation models and the various empirical models are outlined and
discussed.