The relationship between the recovery phase of geomagnetic storms and the magnetic clouds

Abstract Starting with our elliptical cross-section model for the study of the magnetic topology of magnetic clouds (MCs) in the interplanetary medium, we develop an analytical approach to the behavior of the D st index at the recovery phase of a geomagnetic storm. Assuming an axially symmetric ring current, we estimate its physical parameters during that recovery phase of the storm-time. We compare the theoretical and measured D st indexes in two intense geomagnetic storms ( D st