Field‐aligned current signatures during the March 13–14, 1989, Great Magnetic Storm

Abstract

Characteristics of field‐aligned currents (FACs) in the evening and morning regions during the March 13–14, 1989, great magnetic storm have been determined using magnetic and electric field data obtained from the EXOS D spacecraft. This storm began with an SSC at 0128 UT on March 13, and the second SSC occurred at 0747 UT on the same day. The storm continued until March 14. The equatorward boundary of the FAC region began to move equatorward right after the first SSC in both the evening and morning sectors, but the poleward boundary did not immediately respond to the SSC. The equatorward boundary of the FAC system reached as low as below 48° invariant latitude, which corresponds to L = 2.2, and the latitudinal width of the FAC region increased greatly, particularly in the morning sector (∼33° in invariant latitude). In the evening sector the conventional current system characterized by a pair of upward region 1 and downward region 2 FACs changed into complicated patterns consisting of many pairs of upward and downward FACs with the development of the storm, particularly around 22 UT on March 13 when an intense eastward electrojet was observed as low as 50° invariant latitude on the ground. In the morning sector an additional large‐scale upward FAC was observed poleward of the conventional downward region 1 and upward region 2 FAC system throughout the storm. In addition, a pair of FACs with a narrow latitudinal width (∼1.5°) was observed at the poleward boundary of the extra upward FAC.