Ionospheric convection signatures and magnetic field topology

Abstract

We present here a statistical study of signatures of the high‐latitude ionospheric convection pattern and the simultaneously observed energetic electron precipitation. We most often find convection cells in which the sunward flowing region contains auroral particle precipitation but the antisunward flowing region does not. However, our observations also show the frequent occurrence of convection cells in which neither the antisunward nor the sunward flowing plasma region contains auroral particle precipitation. These findings may appear within the dawnside or duskside convection pattern and strongly suggest that such convection cells may be associated with open magnetic field lines that thread the magnetotail lobes. Examination of the interplanetary magnetic field (IMF) data shows that this “lobe cell” convection signature is most likely to be accompanied by the signature of dayside merging when the IMF has a significant y component but is directed southward. A lobe convection cell has a location and sense of circulation that are dependent on the sign of By. For the northern hemisphere, clockwise circulation displaced to the duskside appears roughly 35% of the time when By is positive, and anticlockwise circulation displaced to the dawnside appears when By is negative. The same circulation sense and location exist in the southern hemisphere for the opposite polarity of By. At times of northward IMF, the circulation within the polar cap can be at least partially on closed field lines and cannot be easily reconciled with merely a distortion of the standard “two‐cell” convection pattern. The significance of these results to several models of the solar wind/magnetosphere interaction is discussed.