A very large scale flow burst observed by the SuperDARN radars

We examined the dynamics of the ionospheric plasma in the dayside sector by using the HF radar data at Iceland West and at Finland from 1100 to 1230 U T on September 5, 1995. During that period, the solar wind density was high and the IMF was strongly southward. The dayside magnetopause was highly co mpressed nearly to the geosynchronous orbit. The two radars simultaneously detected a poleward flow burst in the noon sector which, assuming uniformit y of flow in the region of the data gap (1.5 MLT) between the two radars, s howed a magnetic local time extent of 5 hours. This local time extent is 2 to 3 hours wider than previous results. The maximum poleward plasma velocit y of the flow burst is similar to 750 m/s, and the latitudinal size of the flow burst region is similar to 100 to 200 km. This flow burst region initi ally expanded in longitude up to 5 hours, and then shifted poleward with a phase speed of 400 to 670 m/s. The flow burst has a duration of similar to 20 min. This large-scale poleward flow burst is likely to be due to large-s cale reconnection occurring at the dayside magnetopause and subsequent conv ection as the magnetic field lines are transported across the polar cap.