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

Abstract

During the past few years of SuperDARN observations, mesoscale (500–1000 km diameter) clockwise‐sense convection vortices which do not show significant movement in any direction have been observed in the postnoon sector. These convection vortices or small convection cells are herein named quasi‐stationary convection vortices (QSCVs). In this paper, a statistical study of 28 QSCVs is presented, using Saskatoon‐Kapuskasing radar data from the period October 1993 to March 1997. These QSCVs occur in the magnetic latitude interval 72°–81° between 1430 and 1630 magnetic local time (MLT) and are centered near the western end of the afternoon convection cell. The QSCVs occur mainly during southward interplanetary magnetic field (IMF) but sometimes for northward IMF. They appear at lower latitudes as the IMF Bz becomes more negative; they occur at higher latitudes and earlier local times for positive IMF By and at lower latitudes and later local times for negative IMF By. All the QSCVs appear to be associated with large‐amplitude fluctuations either in the IMF or in the solar wind pressure, or in both. It is found that the time of the ionospheric convection change in response to the fluctuations in the IMF and solar wind pressure at the magnetopause is about 6–9 min. The observations have shown some evidence that the termination of the vortex is caused also by large changes in the IMF and/or solar 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 are closely associated with the region 1 field‐aligned currents. Unlike traveling convection vortices, the QSCVs do not appear to be related to any instability at the magnetopause or low‐latitude boundary layer. The large fluctuations in the solar wind pressure and IMF seem to be likely initiating mechanisms for the QSCVs.