Mapping of Field-Aligned Current Patterns during Northward IMF

Summary

Magsat and Ørsted high-precision magnetic measurements have been combined to provide detailed and consistent mapping of ionospheric field-aligned current (FAC) patterns during intervals of northward interplanetary magnetic field (NBZ) conditions. The satellite observations indicate that the NBZ FAC currents extend from two rounded ionospheric regions centered at 85° geomagnetic latitude and magnetic local times of approximately 0900 for the upward and 1500 for the downward FAC. The analysis has revealed that the locations of the NBZ FAC regions are almost invariant to seasonal variations and to variations in the magnitude of IMF B _z . The NBZ FAC currents are sizeable for summer conditions only; they almost vanish during equinox and winter seasons. The NBZ FAC intensity is a strongly non-linear function of IMF B _z rising strongly above a marked threshold at around +5 nT. The observations support experiences from polar magnetometer observations, among other from Greenland, on the gradual development of high-latitude convection changes following IMF changes.