Fig. 2

Four snapshots of the Sq current system (in a form of stream function; in kA) estimated for a quasi-equinoctial day (March 16, 2011). Currents of the northern vortex move counterclockwise, and those of the southern vortex move clockwise. Dashed black lines show geomagnetic latitude ranges (between \(\pm\, 6^{\circ }\) and \(\pm\, 60^{\circ }\)). All observatories used for Sq source estimation lie within these boundaries