Field-aligned Currents Inferred from Low-Altitude Earth-Orbiting Satellites and Ionospheric Currents Inferred from Ground-Based Magnetometers — Do They Render Consistent Results?

Field-aligned currents (FACs) and ionospheric Hall currents were inferred from spatially and temporally coincident vector magnetometer measurements made along the Greenland west coast onboard the Orsted satellite and on the ground, respectively. We selected satellite passes which were closely aligned with the ground-based magnetometer chain, and investigate whether the trajectoryintegrated FAC (TIFAC) is consistent with the ionospheric Hall current across the line of magnetometers. Our analysis builds on the assumption that FACs are closed in the ionosphere via Pedersen currents driven by an electric field which also drives ionospheric Hall currents. Solar radiation conductance models suggest that the Hall/Pedersen conductance ratio, and consequently the Hall/Pedersen current ratio, and eventually the Hall/TIFAC ratio, should be slightly greater than 1. We examined 236 cases covering the midnight-morning-noon sector and found at times small and at other times large deviations from this ratio. We suggest that the latter cases represent conditions where the infinite current sheet assumption is violated or the ionosphere exhibits strong conductivity gradients or conductances are largely caused by charged particle precipitation. Deviations from a ratio of 1 appear to occur predominantly equatorward of ≈74° corrected geomagnetic latitude (CGML) in the midnight sector and poleward of ≈72° in the noon sector.