High‐latitude ionospheric convection pattern during steady northward interplanetary magnetic field

Abstract

The DMSP F8 satellite's coverage of Earth's polar regions provides horizontal ion drift velocities along the dawn‐dusk meridian at approximately 835 km altitude in each hemisphere during the ∼100 min orbital period. We examine the ionospheric convection signatures observed by this spacecraft in the summer and winter hemispheres during periods when the interplanetary magnetic field (IMF) is directed northward for at least 45 min prior to the satellite entering the polar region and remains northward throughout the polar pass. These convection signatures can be readily categorized by the number of sunward and antisunward flow regions and by their potential distributions. Here we describe the most frequently identifiable and reproducible features of the convection pattern that exist during steady northward IMF conditions. In addition to IMF Bz, the influences on the convection pattern of the IMF Bz/|By| ratio, season, latitude, and solar wind velocity are all considered. The ratio Bz/|By| provides a first order organization of the signatures that occur on the dayside of the dawn‐dusk meridian. Sunward flow at highest latitudes on the dayside of the dawn‐dusk meridian is the dominant feature seen in the large‐scale convection signature during steady northward IMF; however, sunward flow at highest latitudes does not imply the existence of a particular number of convection cells.