Nightside polar cap boundary and the auroral electrojets

We present several event studies of the relation between the polar cap boundary (PCB) and the auroral electrojets in the nightside ionosphere. The PCB was determined by the EISCAT incoherent scatter radar measurements and the east-west equivalent electrojets were derived from the MIRACLE magnetometer data by using the 1-D upward continuation. In several cases, the PCB location in relation to the Harang discontinuity was examined, and comparisons to satellite imagery data of the auroral oval were made. For some of the events, the ionospheric reconnection electric field could be estimated as a measure of the nightside reconnection rate and its variation was studied.