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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 condi5 tions. 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 IMF Bz and IMF By variations. 10 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 15 variation with the IMF. According to the statistical models, there is a two-cell anti sunward convection within the polar cap for northward IMF Bz≤2 nT, while for increasing northward IMF Bz+ 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 IMF Bz+ ≈ 4-5 nT. This results in a four-cell convection pattern of the 20 high-latitude convection. In dependence of the +_ IMF By contribution during sufficiently strong northward IMF Bz conditions, a transformation to three-cell convection patterns takes place.