An analysis of neutral wind generated currents during geomagnetic storms

High latitude field-aligned currents generated by neutral winds during and after a strong geomagnetic storm have been investigated to elucidate geophysical conditions that limit the development of these currents. The coupled magnetosphere-ionosphere-thermosphere (CMIT) model is used in this study. It is found that post-storm, neutral-wind-driven currents are smaller than those generated during the storm due primarily to the reduction of ionospheric conductivity. In addition, the storm enhanced ionospheric conductivity occurs mostly in the lower thermospheric region, whereas the strongest storm-enhanced neutral winds occur at higher altitudes. This mismatch between the peaks of the ionospheric conductivity and the storm enhanced neutral winds limits the development of the neutral wind generated field-aligned currents and thus their effects on M-I coupling. It is also found that neutral wind field-aligned current is generated in a thin layer just above the Pedersen conductivity peak where significant conductivity and stormed enhanced neutral wind co-exist. The contribution from the upper thermospheric neutral wind is a minor factor because of the lower conductivities there.