HIGH-LATITUDE IONOSPHERIC CONVECTION PATTERN DURING STEADY NORTHWARD INTERPLANETARY MAGNETIC-FIELD

The DMSP F8 satellite's coverage of Earth's polar regions provides hor izontal ion drift velocities along the dawn-dusk meridian at approxima tely 835 km altitude in each hemisphere during the similar to 100 min orbital period. We examine the ionospheric convection signatures obser ved by this spacecraft in the summer and winter hemispheres during per iods when the interplanetary magnetic field (IMF) is directed northwar d for at least 45 min prior to the satellite entering the polar region and remains northward throughout the polar pass. These convection sig natures can be readily categorized by the number of sunward and antisu nward flow regions and by their potential distributions. Here we descr ibe the most frequently identifiable and reproducible features of the convection pattern that exist during steady northward IMF conditions. In addition to IMF B-z, the influences on the convection pattern of th e IMF B-z/\B-y\ ratio, season, latitude, and solar wind velocity are a ll considered. The ratio B-z/\B-y\ 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 me ridian is the dominant feature seen in the large-scale convection sign ature during steady northward IMF; however, sunward flow at highest la titudes does not imply the existence of a particular number of convect ion cells.