Ionospheric midlatitude electric current density inferred from multiple magnetic satellites

A method for inferring zonal electric current density in the mid-to-low latitude F-region ionosphere is presented. We describe a method of using near-simultaneous overflights of the Ørsted and CHAMP satellites to define a closed circuit for an application of Ampère’s integral law to magnetic data. Zonal current density from sources in only the region between the two satellites is estimated for the first time. Six years of mutually available vector magnetic data allows overlaps spanning the full 24-hour range of local times twice. Solutions are computed on an event-by-event basis after correcting for estimates of main and crustal magnetic fields. Current density in the range ±0.1μA/m^2 is resolved, with the distribution of electric current largely matching known features such as the Appleton anomaly. We also resolve a new ionospheric feature: persistent current intensifications between geomagnetic latitudes of 30 and 50 degrees in the post-midnight, pre-dawn sector. We compare our results with current density predictions made by the Coupled Thermosphere-Ionosphere-Plasmasphere (CTIP) model, a self consistent, first-principles, 3-dimensional numerical dynamic model of ionospheric composition and temperatures. This independent validation of our current density estimates highlights good agreement in the broad spatiotemporal trends we identify, which increases confidence in our results.