Field‐aligned currents in the dayside cusp and polar cap region during northward IMF

Abstract

The field‐aligned currents in the dayside cusp and polar cap region are examined using magnetic data from the low‐altitude polar‐orbiting satellite Ørsted. The study is confined to cases where the interplanetary magnetic field (IMF) has a steady northward component and to a rather narrow region spanning ∼4 hours around magnetic noon. We examine individual passes using a maximum variance analysis method, and we complement, for a single event, with ground‐based data from the Greenland meridian chain of magnetometers. We suggest that when an east‐west component By of the IMF exists for positive IMF Bz, the two NBZ (northward Bz) field‐aligned currents that prevail over the polar region rotate to form the two field‐aligned currents equatorward and poleward of the east‐west flowing ionospheric DPY current in the dayside. The high accuracy of the Ørsted data makes it possible to uncover details not previously described.