Characteristics of eastward drifting omega bands in the morning sector of the auroral oval

Abstract

The STARE radars and the Scandinavian networks of magnetometers, all‐sky cameras, and riometers recorded during the night of October 21/22, 1979, the occurrence of a fairly regular sequence of auroral omega bands and associated magnetic and electric field variations. The combined two‐dimensional data are used to derive a realistic model for the three‐dimensional current flow associated with the auroral forms. In the model calculations the observed structure in the particle precipitation is accounted for by an inhomogeneous ionospheric conductivity distribution. The main resulting feature of the model current system is a sequence of east–west orientated pairs of upward and downward directed field‐aligned currents, associated with the bright and dark areas of the visual aurora, respectively. The major source of magnetic disturbances on the ground is a “meandering” ionospheric Hall current, composed of a westward background electrojet and circular Hall current vortices around the locations of the localized field‐aligned currents. The total magnetic disturbance observed on the ground during different events appears, however, to be strongly dependent on the Hall to Pedersen conductivity ratio and the degree of inhomogeneity in the conductivity distribution. The three‐dimensional current system associated with the auroral omega bands drifts eastward with a velocity comparable to an E × B drift within the general southward directed electric background field. However, complete agreement was not found at all times.