SuperDARN observations of quasi-stationary mesoscale convection vortices in the dayside high-latitude ionosphere

During the past few years of SuperDARN observations, mesoscale (500-1000 km diameter) clockwise-sense convection vortices which do not show significan t movement in any direction have been observed in the postnoon sector. Thes e convection vortices or small convection cells are herein named quasi-stat ionary convection vortices (QSCVs). In this paper, a statistical study of 2 8 QSCVs is presented, using Saskatoon-Kapuskasing radar data from the perio d October 1993 to March 1997. These QSCVs occur in the magnetic latitude in terval 72 degrees-81 degrees between 1430 and 1630 magnetic local time (MLT ) and are centered near the western end of the afternoon convection cell. T he QSCVs occur mainly during southward interplanetary magnetic field (IMF) but sometimes for northward IMF. They appear at lower latitudes as the IMF B-z becomes more negative; they occur at higher latitudes and earlier local times for positive IMF B-z and at lower latitudes and later local times fo r negative IMF B-z. All the QSCVs appear to be associated with large-amplit ude fluctuations either in the IMF or in the solar wind pressure, or in bot h. It is found that the time of the ionospheric convection change in respon se to the fluctuations in the IMF and solar wind pressure at the magnetopau se is about 6-9 min. The observations have shown some evidence that the ter mination of the vortex is caused also by large changes in the IMF and/or so lar wind pressure. The lifetime of the QSCVs is typically 10-20 min, but it can be as long as 50 min. The QSCVs have clockwise rotational sense and ar e closely associated with the region 1 field-aligned currents. Unlike trave ling convection vortices, the QSCVs do not appear to be related to any inst ability at the magnetopause or low-latitude boundary layer. The large fluct uations in the solar wind pressure and IMF seem to be likely initiating mec hanisms for the QSCVs.