Does the South Atlantic Anomaly influence the ionospheric Sq current system? Inferences from analysis of ground-based magnetic data

Abstract

We study if and how the South Atlantic Anomaly influences the ionospheric solar quiet (Sq) current system. Geomagnetically quiet days are processed for the years 1990 and 2011, and the Sq foci tracks are analyzed. The two datasets allow to investigate the influence of the observatory network and the solar activity on the Sq source determination. The computed tracks result in pronounced bands in the northern and southern hemisphere, which seem to neither follow the geographic nor the geomagnetic or dip equator. Remarkably, we observe a distinct scattering of the tracks over the South Atlantic Anomaly. This systematic scattering is due to a larger shift of the southern hemisphere focus northwards during the northern summer solstice and southwards during the southern summer solstice. The physical mechanism of this systematic effect remains unclear. The longitudinal variations of the Sq foci are believed to have their origin from an influence of non-migrating tides as reported in recent studies and the anomalous weak amplitude of the geomagnetic main field over the South Atlantic Anomaly.