PERIODIC LONGITUDINAL STRUCTURE OF FIELD-ALIGNED CURRENTS IN THE DAWNSECTOR - LARGE-SCALE MEANDERING OF AN AURORAL ELECTROJET

The azimuthal structure of field-aligned current (FAC) systems is one of the target subjects of the Freja satellite's magnetometer observati on. In the event of May 28, 1993, the satellite observed large-amplitu de fluctuations of the latitudinal, as well as the longitudinal, magne tic field components along a postmidnight-to-morning orbit. By combini ng radar and ground magnetometer data, we inferred that the associated FAC system has a periodic structure consisting of multiple FAC sheets inclined significantly from the azimuthal (east-west) direction and m oving westward and possibly poleward. Such a structure may be interpre ted in terms of the meandering of an auroral electrojet, and perhaps a s the ionospheric projection of boundary waves.