Observations of Field-Aligned Currents and Particle Precipitation Patterns During Events of Strongly Northward IMF

We have used the combination of Magsat and Oersted high-precision magnetic measurements to provide detailed and consistent patterns of ionospheric field-aligned current (FAC) patterns during intervals of northward interplanetary magnetic field (NBZ) conditions. Our analysis has revealed that the NBZ FAC currents extend from two rounded or bean-shaped ionospheric regions centered at 85 deg geomagnetic latitude and magnetic local times of approximately 0900 for the upward and 1500 for the downward FAC. The locations of the NBZ FAC regions are almost invariant to seasonal variations and to variations in the magnitude of IMF Bz. The NBZ FAC currents are sizeable for summer conditions only and vanish during equinox and winter seasons. The NBZ FAC intensity is a strongly non-linear function of IMF Bz with a marked threshold at around +5 nT. We have further used magnetometer observations from Greenland to investigate the development of high-latitude convection patterns following rapid IMF changes and we have used high-energy particle observations from satellites and from ground to investigate the related changes in magnetospheric configuration. These observations and their interpretation in terms of solar wind-magnetosphere-ionosphere coupling will be presented in this paper.