Zonal variation of ionospheric radial current (IRC) as observed by Swarm and simulated by TIE-GCM

 Based on the magnetic field observation of Swarm satellite from 2015 to 2019, the variation of ionospheric radial current (IRC) with local time and geographic longitude at March equinox, June solstice and December solstice are analyzed, respectively. The observations are compared with the simulation results of thermosphere ionosphere electrodynamics general circulation model (TIE-GCM). The observed IRC are mainly downward in the noon section and upward in the evening section, which is reproduced well by the model. The zonal distribution of IRC shows obvious local time asymmetry. The downward IRC in the eastern hemisphere in the noon section is greater than that in the western hemisphere, while the upward IRC in the western hemisphere in the evening section is greater than that in the eastern hemisphere. This zonal variation in the evening sector is more obvious at March equinox and less obvious at June solstice. The simulation results of TIE-GCM also show similar zonal characteristics, especially on the nightside. The physical mechanisms of the local time and geographic longitude distribution of IRC are discussed in details.