High-latitude plasma convection during Northward IMF as derived from in-situ magnetospheric Cluster EDI measurements

摘要: In this study, we investigate statistical, systematic variations of the high-latitude convection cell structure during northward IMF. Using 1-min-averages Cluster/EDI electron drift observations above Northern and Southern polar cap areas for six a half years (February 2001 till July 2007), mapping spatially distributed measurements to common reference plane at ionospheric level in magnetic latitude/MLT grid, obtained regular patterns according various IMF conditions. We focus on particular conditions IMF, where lobe cells latitudes >80° with opposite (sunward) over central are permanent feature addition main lower latitudes. They due reconnection processes magnetopause boundary poleward cusp regions. Mapped EDI data have good coverage within part cap, so that these their dependence solar wind well verified statistical sense. On average, 4-cell pattern shown as structures periods nearly tendency small shift toward negative clock angles. The positions foci 79° 85° latitude 09:00–15:00 MLT. MLT approximately symmetric ±2 h about 11:30 MLT, i.e. slightly offset from midday prenoon hours, while maximum (minimum) potential is higher near difference ≈−10° −15° angle North (South) Hemisphere. With increasing distances ≈IMF B z +, gradual transition occurs via 3-cell 2-cell pattern, course which one medium-scale dayside diminishes disappears other intensifies merges same polarity form large "round-shaped" when approaching well-known y -dominated configuration. Opposite scenarios interchanged roles respective occur turning become more pronounced magnitude vector.