IMF By effects in the magnetospheric convection on closed magnetic field lines

Using data from the Super Dual Auroral Radar Network (SuperDARN) and the ultraviolet imager on the Polar satellite, we have earlier shown that the IMF By-related electric field can penetrate into the closed magnetosphere and produce convection changes in the region of the postnoon auroral oval [Kozlovsky et al., JGR, N12, 2002]. In such a case, contra-directed azimuthal (East-West) plasma flows should be expected in the conjugated hemispheres. In this paper we present a theoretical model, which can well explain these observations. Due to the solar wind-magnetosphere dynamo, IMF By generates a voltage between the two polar caps, so that field-aligned currents flow between the two hemispheres within some layer just equatorward of the open polar cap boundary. In this region a field-aligned potential difference (i.e., a magnetic field line discontinuity) can occur when the field-aligned current exceeds a threshold value. The IMF By-related contra-directed ionospheric plasma flows can co-exist in the northern and southern hemispheres within the region of the inter-hemispheric field-aligned currents. The latitudinal width of this region depends on the IMF By and the ionospheric conductance, and can be of the order of 1-2 degrees.