Evidence for the geomagnetic gradient induced current in the ionosphere around the South Atlantic Anomaly

Abstract

The geomagnetic gradient induced current (GGIC) should exist as a result of the electron and ion drift motions due to the geomagnetic field gradient in the Earth's ionosphere. GGICs exhibit a westward flow near the magnetic equator, whereas around the southern boundary of the South Atlantic Anomaly (SAA), they shift to an eastward direction. These GGICs contribute to the strongest radially outward magnetic field near the center of the SAA. This GGIC-induced magnetic field is easily contaminated by the solar quiet (Sq) currents and equatorial electrojet, so that it usually cannot be directly verified from the magnetic field measurements. By subtracting the CHAMP, Ørsted, and SAC-C model of Earth's magnetic field from Swarm satellites' magnetic field measurements, the magnetic fields produced by the ionospheric currents are illustrated. To eliminate the influence of other currents, we calculate the radial magnetic field differences between the summer and winter seasons in the southern hemisphere using data from all three Swarm satellites. This differential magnetic signature, which points radially outward, can only be attributed to the GGIC. Despite the limited measurements, the existence of GGIC can be also verified in the radial magnetic field data collected by the Macao Science Satellite-1. Our results reveal a universal phenomenon that occurs in the dayside ionospheres of the magnetized planets.