Reproducing the electric current system in the polar ionosphere by emulator-based data assimilation

The ionospheric electric currents are a principal source of geomagnetic variations and geomagnetically-induced currents (GICs) in the polar region. It is therefore essential to model the polar ionospheric electric currents to discuss the geomagnetic phenomena at high latitudes. Recently, we have developed a data assimilation system based on an emulator of a global magnetohydrodynamic (MHD) model of the magnetosphere. In this system, line-of-sight velocity data by the SuperDARN radars are incorporated into the emulator using a data assimilation method based on the ensemble transform Kalman filter, and it estimates the electric potential distribution in the polar ionosphere by exploiting both physical knowledge and observational information. In this study, we derived the spatial distributions of the ionospheric currents and field-aligned currents (FACs) from the potential distribution obtained from the data assimilation system. The results well reproduced typical features of the ionospheric currents such as DP2 two-cell patterns and those of the FACs such as the Region-1 and Region-2 systems. This framework is promising for analyzing various phenomena in the polar ionosphere.