Ionospheric electrodynamic response to solar flares in September 2017

In this work, the Thermosphere-Ionosphere-Electrodynamics General Circulation Model is used to investigate the responses of ionospheric electrodynamic processes to the solar flares at the flare peaks and the underlying physical mechanisms on September 6 and 10, 2017. Simulations show that solar flares increased global daytime currents and reduced the eastward electric fields during the daytime from the equator to middle latitudes. Furthermore, westward equatorial electric fields and equatorial counter electrojets occurred in the early morning. At the flare peak, these electrodynamic responses are predominantly related to the enhanced E-region conductivity by flares, as the responses of neutral winds and F-region conductivity to flares are negligible. Specifically, the Cowling conductance enhancement is not the major process causing the reduction of zonal electric fields. This electric field reduction is primarily associated with the decrease of the ratio between the field line-integrated wind-driven currents and the conductance. The flare-induced conductivity enhancement is larger but the background wind speed is smaller in the E-region than in the F-region, as a result, the increase of total integrated wind-driven currents is less than the conductance enhancement.