Magnetospheric convection from Cluster EDI measurements compared with the ground-based ionospheric convection model IZMEM

Abstract. Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for more than seven and a half years (2001–2008) have been used to derive a statistical model of the high-latitude electric potential distribution for summer conditions. Based on potential pattern for different orientations of the interplanetary magnetic field (IMF) in the GSM y-z-plane, basic convection pattern (BCP) were derived, that represent the main characteristics of the electric potential distribution in dependence on the IMF. The BCPs comprise the IMF-independent potential distribution as well as patterns, which describe the dependence on positive and negative IMFB_z and IMFB_y variations. The full set of BCPs allows to describe the spatial and temporal variation of the high-latitude electric potential (ionospheric convection) for any solar wind IMF condition near the Earth's magnetopause within reasonable ranges. The comparison of the Cluster/EDI model with the IZMEM ionospheric convection model, which was derived from ground-based magnetometer observations, shows a good agreement of the basic patterns and its variation with the IMF. According to the statistical models, there is a two-cell antisunward convection within the polar cap for northward IMFB_z+≤2 nT, while for increasing northward IMFB_z+ there appears a region of sunward convection within the high-latitude daytime sector, which assumes the form of two additional cells with sunward convection between them for IMFB_z+≈4–5 nT. This results in a four-cell convection pattern of the high-latitude convection. In dependence of the ±IMFB_y contribution during sufficiently strong northward IMFB_z conditions, a transformation to three-cell convection patterns takes place.