Variations of Inner Magnetospheric Currents During the Magnetic Storm of May 1998

Abstract

AbstractTransient variations of the geomagnetic field at low latitudes are mainly caused by the following current systems: the ionospheric dynamo current (IDC), the symmetrical ring current (SRC), and the 3D partial ring current system (PRFI). Meanwhile, the region I ield aligned current‐ionospheric current system (FACI) annot be ignored. In this paper, the ariations of these current systems during the large storm on May 1‐6, 1998 are discussed. The disturbances of the storm contains two events. One is during May 1‐3 and the other is during May 4‐5. The Sq‐field caused by IDC is calculated by using several station pairs. Then, the fields of other sources are separated by fitting data to their field models. Results show that: (1) PRFI and FACI do not develop significantly in the first event, while they develop strongly with substorms in the second event. (2) The variations of SRC‐field are similar to Dst index in the first event and delayed to Dst in the second event. (3) In the second event, PRFI develops before SRC, and SRC depresses associated with the recovery of PRFI and FACI. These results provide a clue to understand the formation of the ring current and field‐aligned currents and their relationship.