Local time and longitudinal variation of the ionospheric radial current: Swarm observations and TIE-GCM simulations

Based on the high-precision vector magnetic field data of Swarm A and C satellites, we perform a statistical analysis of the diurnal and longitudinal variations of the ionospheric radial current (IRC) in the F layer at the magnetic equator from 2014 to 2018. The observations are compared with the simulations based on the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM). It is found that the noon IRC is radially outward, whereas the dusk IRC is radially inward. The time of the change from the inward to the outward direction occurred is earlier in June than in other seasons. The TIE-GCM results show that low atmospheric tides have an important effect on the seasonal change in the reverse time. The noon IRC is weakened primarily by the polarization current from migrating tides. The dusk IRC is mainly weakened by polarization current from nonmigrating tides in the equinox and December solstice and by dynamo current from migrating tides in the June solstice. Geomagnetic field configuration is the main reason for the longitudinal variation of IRC. The noon IRC have a wave-4 zonal structure, which is mainly caused by the outward propagation of migrating and nonmigrating tides. The dusk IRC in the western hemisphere shows a larger current density than that in the eastern hemisphere, resulting mainly from the neutral wind dynamo current. The competing effect of the wind dynamo current and polarization current determined the peak location of the total current in the western hemisphere.