Electric currents above Saint‐Santin: 3. A preliminary study of disturbances: June 6, 1978; March 22, 1979; March 23, 1979

This paper presents three case studies of ionospheric disturbances in electric fields, currents, and winds during periods of geomagnetic storms. These disturbances are detected by the Saint‐Santin incoherent scatter radar. The disturbances are shown to originate from two distinct physical mechanism: (1) penetration of electric fields to lower latitudes during times of rapid change in magnetospheric convection; and (2) the action of the disturbed ionospheric dynamo driven by storm‐induced wind disturbances. The storm of June 6, 1978, shows a simple illustration of penetrative convection electric fields. The storm of March 22, 1979, gives additional examples of this effect both when the B z component of the interplanetary fields turns southward and northward. The observed events on March 23 are clearly identifiable as the delayed response of the disturbance ionospheric dynamo.