Fast Auroral Evolution and Related Magnetic Field Changes on the Ground and at Conjugate Satellites

Abstract

Auroral activities on January 7, 1986, are examined with all-sky video data obtained at multiple stations. It is shown that a poleward expansion front of an expansion aurora usually consists of many northwestward protrusions which develop and decay here and there during the course of the auroral expansion. Developments of characteristic auroral protrusions are compared with magnetic field changes on the ground. The result shows that the developments of large magnetic field deflections on the ground are most likely due to enhancements of local westward electrojets associated with counterclockwise vortex currents around developing auroral protrusions in the night sector. The developments of auroral protrusions are also related to magnetic field changes at the synchronous satellites, GOES 5 and 6, conjugate with the auroral forms. Characteristic changes of magnetic field occur at GOES 5 and 6 concurrently with developments of auroral protrusions around respective magnetic footpoints of the satellites. Auroral structures within or in the vicinity of auroral protrusions are likely interlinked with the field-aligned currents around the conjugate synchronous satellites.