IMF By-related cusp currents observed from the Ørsted satellite and from ground



Ørsted is the first satellite to conduct high-precision magnetometer observations from low-altitude noon-midnight orbits passing through the polar cusp regions. Field-aligned currents (FAC) derived from Ørsted magnetic field measurements have been combined with ionospheric current patterns inferred from ground-based magnetic observations to define the structure and location of cusp currents and their dependencies on interplanetary magnetic field (IMF) conditions. Example cases illustrate the close relation between IMF By-related FAC and horizontal ionospheric currents in the cusp region. Our statistical analysis defines for the noon region the variations in FAC latitude with IMF Bz. Comparisons with the statistical cusp location indicate that the more equatorward region of IMF By-related FAC is located on field lines closing at the dayside, while the more poleward FAC are on “open” field lines. High-energy electron measurements from the satellite confirm this result.