Cause of the preliminary reverse impulse of storms

Atmospheric-current functions obtained for sudden commencements by Nagata and Abe, and by Jacobs and Obayashi, are analyzed. Electric-charge distributions in the ionosphere are deduced that could drive the part of the currents asymmetric about the geomagnetic axis. It is supposed, as an approximation, that only the Hall electric conductivity need be taken into account. Distortions of the outer magnetosphere that may give rise to the reverse impulse are discussed.