Seasonal effect for polar cap sunward plasma flows at strongly northward IMF B_z

Abstract

We use Super Dual Auroral Radar Network data to study polar cap ionospheric flow under strongly dominant positive interplanetary magnetic field B_z component. We show that the near-noon flow along the magnetic meridian is predominantly sunward in summer. The sunward velocity increase with intensification of the external driver (the reverse convection electric field) is also faster in summer, and the rate of the increase is slightly larger for the Southern Hemisphere. The sunward flows simultaneously detected in both hemispheres are faster in the summer hemisphere. In addition, while sunward flows are aligned with the midnight-noon line in a winter hemisphere, they are oriented toward earlier magnetic local hours in a summer hemisphere.