Influence of the Polar Electrojet on Field‐Aligned Current Estimates From Single Satellite Magnetic Field Measurements

Abstract

AbstractThe high‐resolution magnetic field measurements from European Space Agency's (ESA’s) Swarm satellite constellation provide a good opportunity for revisiting the mean properties of ionospheric currents. Among the Swarm Level‐2 data products, provided by European Space Agency, are field‐aligned current (FAC) estimates based on single‐spacecraft (single‐SC) and dual‐spacecraft (dual‐SC) solutions. For the more reliable dual‐SC approach only magnetic signatures from currents flowing through the integration loop are considered, while in the case of single‐SC FAC estimates the magnetic effects of all remote current systems contribute to the results. A direct comparison between the two FAC products at auroral latitudes reveals that the single‐SC estimates systematically overestimate the current density of region 2 (R2) FACs by about 15%, while underestimates the region 1 (R1) FACs by about 10%. The differences between the two FAC products appear closely related to the location and direction of the horizontal polar electrojet (PEJ) at auroral latitudes. A direct comparison of these two current systems suggests an influence of the PEJ induced magnetic field on the solutions from single‐SC FACs. Our preferred explanation is the effect of a partial diversion of the anti‐sunward flowing electrojet current into the polar cap region. The current deflection angle increases toward the pole. The B‐field of such a current flow geometry can explain the single‐SC differences. It is consistent with the general picture of the high‐latitude Hall current vortices. As a side aspect, we found that the mean PEJ intensities are almost identical in both hemispheres, but the latitudes of the current peaks differ between the two hemispheres in the morning/afternoon sectors by about 1°. The reason for this difference is not clear.