Vertical total electron content and geomagnetic perturbations at mid- and sub-auroral southern latitudes during geomagnetic storms

The AL index and the geomagnetic field variations allow us to recognize the expansion phase of the substorm due to the presence of the electromagnetic wedge that couples the magnetosphere and ionosphere at high latitudes. Fluctuations in the VTEC computed from the GPS observatories are in rough agreement with the influence of the upward and downward field-aligned currents of the wedge.