Filamentary structure of the westward electrojet in the midnight sector auroral distribution during substorms: comparison with Viking auroral observations

Abstract

The relationship between equivalent electric currents, auroral absorption and aurora structures in the midnight auroral distribution is examined using the ground magnetic and riometer observations along the Kara meridional chain of stations and auroral images obtained by the Viking spacecraft. Equivalent currents are calculated by the method of Kotikov et al. [(1987) Geophysica 23, 143] on the basis of the magnetic data. A filamentary structure of westward currents is found in the midnight auroral electrojet during substorm expansion phase. This structure develops in the poleward part of the auroral distribution only in those cases when intense auroral absorption spreads to the appropriate latitudes, and these structured westward currents are observed in areas where the UV auroral luminosity is high. Justifications that the calculated equivalent currents are real ionospheric currents are presented. Calculation of the ionospheric conductivity based on the measurements of precipitating electrons from DMSP-F7 shows that the conductivity in the regions of the westward filaments is enhanced.