SuperDARN‐detected plasma convection vortices and the global plasma convection

Abstract

Routine Super Dual Auroral Radar Network (SuperDARN) ionospheric plasma convection maps were used to assess the performance of the Weimer 96 model, which predicts a convection pattern for the entire high‐latitude ionosphere for any value of the interplanetary magnetic field (IMF) By and Bz components, the solar wind speed, and the seasonal dipole tilt angle. Reasonable agreement between model predictions and SuperDARN measurements are shown for the most typical IMF orientations on the clock diagram and moderate IMF intensities between 1 nT and 5 nT. Global convection patterns were then derived for the periods when the SuperDARN HF radars detected mesoscale quasi‐stable convection vortices. The earlier finding that convection vortices with clockwise (CW) plasma circulation occur at the dayside ends of large‐scale dusk convection cells (for Bz < 0) was confirmed, but only for 9 events out of 25 events that were studied. We found that vortices can occur at the dayside ends of dawn convection cells. The sense of plasma circulation in these vortices is counterclockwise (CCW). We also found that CW and CCW convection vortices can occur, though rarely, at the night ends of large‐scale convection cells, dusk and dawn, respectively. We found that in 11 vortex events out of all events studied the SuperDARN maps were simply showing plasma circulation around the foci of the global convection cells (Bz > 0 and Bz < 0). For strongly northward IMF, there were located two vortex events for which vortices represented the entire cell in a multicell global plasma convection pattern. These results indicate that different mechanisms for vortex formation should be considered, depending on what kind of vortex has formed.