Magnetospheric substorm‐related electric fields in the ionosphere: Discrepancy of an observation with model predictions

Abstract

Theoretical models of disturbance electric fields in the middle and low latitude ionosphere have successfully explained several observed characteristics of the above electric fields. The models generally predict a large westward electric field in the 2300 – 0400 LT sector; but a recent study of a major F‐region disturbance at mid‐latitudes revealed a large east‐ward electric field in the midnight‐to‐morning sector, during a magnetospheric substorm. This discrepancy indicates that processes additional to those considered in the models so far are playing an important role during substorms. One possible process is the generation of large, secondary ionospheric electric fields in and around the auroral zone due to the interplay of the spatially varying and time‐varying enhanced conductivities, currents and electric fields during substorms. A second process may be the generation of large secondary electric fields in the inner magnetosphere due to the large spatial gradients of particle drifts during the substorm‐time unsteady convection. During substorms, such secondary electric fields may be dominant, in comparison with the effects of the large scale magnetospheric convection electric field and field‐aligned currents treated successfully in the models.