SUPERDARN-DETECTED PLASMA CONVECTION VORTICES AND THE GLOBAL PLASMA CONVECTION

Routine Super Dual Auroral Radar Network (SuperDARN) ionospheric plasm a convection maps were used to assess the performance of the Weimer 96 model, which predicts a convection pattern for the entire high-latitu de ionosphere for any value of the interplanetary magnetic field (IMF) B-y and B-z components, the solar wind speed, and the seasonal dipole tilt angle. Reasonable agreement between model predictions and SuperD ARN measurements are shown for the most typical IMF orientations on th e clock diagram and moderate IMF intensities between 1 nT and 5 nT. Gl obal convection patterns were then derived for the periods when the Su perDARN KF radars detected mesoscale quasi-stable convection vortices. The earlier finding that convection vortices with clockwise (CW) plas ma circulation occur at the dayside ends of large-scale dusk convectio n cells (for B-z < 0) was confirmed, but only for 9 events out of 25 e vents that were studied. We found that vortices can occur at the daysi de ends of dawn convection cells. The sense of plasma circulation in t hese vortices is counterclockwise (CCW). We also found that CW and CCW convection vortices can occur, though rarely, at the night ends of la rge-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 conve ction cells (B-z > 0 and B-z < 0). For strongly northward IMF, there w ere located two vortex events for which vortices represented the entir e cell in a multicell global plasma convection pattern. These results indicate that different mechanisms for vortex formation should be cons idered, depending on what kind of vortex has formed.