Flow transients in the postnoon ionosphere: The role of solar wind dynamic pressure

Super Dual Auroral Radar Network (SuperDARN) HF radar, magnetometer, and satellite data are used to study ionospheric convection flow bursts in the sunward return flow in the 1200–1500 MLT auroral region. A comparison between the latitudinal position of the flow bursts and the position of the open/closed field line boundary shows that the sunward bursts occur on closed field lines. The bursts occur simultaneously with poleward motions of the convection reversal boundary. Decreases in the solar wind dynamic pressure are shown to correlate well with the flow bursts. Comparison of radar arid magnetometer data shows that these observations can be explained in terms of the global current model proposed for sudden expansions of the rnagnetosphere [Araki and Nagano, 1988]. The sunward flow bursts are shown to be consistent with the high-latitude dusk to dawn electric field predicted by the model during pressure decreases.