Strong flow bursts in the nightside ionosphere during extremely quiet solar wind conditions

Results of an HF radar study of convection during an extended quiet solar wind interval on March 10 1997 are presented. After thirty hours during which the solar wind met the criteria for quiet conditions the HF radars at Sanae and Halley in Antarctica showed strong activity on the night side. Flow bursts with velocities of more than 2000 m s−1, corresponding to electric fields exceeding 100 m V m−1 were observed. These occurred quasi-periodically for almost two hours on the night-side with a repetition time of several minutes. It is concluded that they map to a region well inside the magnetotail. It is suggested that they are associated with sporadic energy release during reconfiguration of the tail magnetic field, and that this can occur even during an extended quiet solar wind period.