Magnetosphere-ionosphere coupling via prescribed field-aligned current simulated by the TIEGCM

A. Maute, A.D. Richmond, G. Lu, D. Knipp, Y. Shi, B. Anderson assert that the 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. Assimilative models have the advantage that the ion convection and auroral particle precipitation patterns are mutually consistent and based on available observations. However, assimilating a large set of diverse data requires expert knowledge and is time consuming. Empirical models, on the other hand, are convenient to use, but do not capture all the observed spatial and temporal variations. With the availability of AMPERE data, there is an opportunity for employing field-aligned currents (FAC) in numerical models to represent the MI coupling.  In this study, we introduce a new method  using observed FAC  and solve for the interhemispherically asymmetric electric potential distribution. We compared geomagnetic storm simulations using the new approach and two other often-used methods for specifying MI coupling based on empirical and assimilative high latitude electric potentials. The comparison shows general similarities of the thermosphere-ionosphere storm time response and  improved temporal variability of the new method compared to using empirical models, but results also illustrate substantial differences due to our uncertain knowledge about the MI coupling process.