Interhemispheric observations of dayside convection under northward IMF

The reverse convection potential and electric field under northward interplanetary magnetic field (IMF) has been shown to saturate at a larger value in the summer than in the winter. Previous studies of reverse convection under northward IMF have suggested that in the winter hemisphere, much of the reconnection involves "internal reconnection" with over-draped field lines from the summer hemisphere. We present a case study in which reverse convection was simultaneously visible in the northern and southern hemispheres near the northern winter solstice. We use SuperDARN radar velocity measurements to demonstrate that the sunward (reverse) convection along the noon meridian is significantly faster in the summer hemisphere. We also use DMSP energetic particle data to demonstrate that in the winter hemisphere, some of the convection circulates on closed field lines, which is a signature of internal reconnection. These results suggest that internal reconnection is much less effective in transmitting the interplanetary electric field (IEF) into the ionosphere.