Field-aligned current distribution at high latitude: Results from the Swarm satellite constellation

Abstract:

ESA’s constellation mission Swarm provides the opportunity to derive more reliable FAC estimates from multi-satellite magnetic field measurements. We make use of the Swarm A/C satellite pair, which flies side-by-side at a separation of 1.4° in longitude. By considering along-track differences over 5 s the four readings at the corners of an almost symmetrical quad are used for calculating the mean vertical current density flowing through the encircled area. FACs are estimated by mapping the vertical current component onto the field direction. Within the auroral oval current estimates from single and dual-satellite solutions agree generally well. Significant differences are frequently observed in the polar cap. Here underlying assumptions for single-satellite solutions are obviously not well satisfied. We compare these polar cap FACs with observations from other satellites. FACs do appear preferably during times of northward IMF, and By seems to play an important role. Other supporting observations come from DMSP satellites. Their particle data and auroral images help to identify the region in the magnetosphere where the FACs are connected to.