Can we simulate magnetosphere-ionosphere coupling via field-aligned current in GCMs?

Magnetosphere-ionosphere (MI) coupling is crucial in modeling the thermosphere-ionosphere (TI) response to geomagnetic activity. In general circulation models (GCMs) the MI coupling is typically realized by specifying the ion convection and auroral particle precipitation patterns from, e.g., empirical or assimilative models. Using assimilative models, such as the Assimilative Mapping of Ionospheric Electrodynamics (AMIE), has the advantage that the ion convection and auroral particle precipitation patterns are self-consistently obtained from available observations. However, assimilating a large set of diverse data can be time consuming and requires expert knowledge, and therefore it is so far not the standard way of MI coupling in GCMs. With the availability of AMPERE data, there is an increased interest of employing field-aligned currents (FAC) in GCMs to represent the MI coupling. The FAC from AMPERE captures interhemispheric differences in the MI coupling not represented by empirical ion convection models. However, since GCMs mostly employ prescribed high latitude ion convection patterns little is known about differences in the TI response to high latitude forcing by prescribed FACs.

In this presentation, we will introduce a method to simulate MI coupling in GCMs via FAC considering interhemispheric differences. We employ FAC derived from AMPERE observation and compare results from a geomagnetic storm simulation to different MI coupling methods: Weimer ion convection and AMIE. With the help of this comparison, we will highlight advantages and challenges of using FAC in MI coupling. We will illustrated that using FAC forcing the hemispheric asymmetry In integrated Joule heating is more pronounced than using Weimer ion convection patterns. We will specifically focus on the high latitude region but also allude to effects at middle and low latitudes.