FILAMENTARY STRUCTURE OF THE WESTWARD ELECTROJET IN THE MIDNIGHT SECTOR AURORAL DISTRIBUTION DURING SUBSTORMS - COMPARISON WITH VIKING AURORAL OBSERVATIONS

The relationship between equivalent electric currents, auroral absorpt ion and aurora structures in the midnight auroral distribution is exam ined using the ground magnetic and riometer observations along the Kar a meridional chain of stations and auroral images obtained by the Viki ng spacecraft. Equivalent currents are calculated by the method of KOT IKOV et al. [(1987) Geophysica 23, 143] on the basis of the magnetic d ata. A filamentary structure of westward currents is found in the midn ight auroral electrojet during substorm expansion phase. This structur e develops in the poleward part of the auroral distribution only in th ose cases when intense auroral absorption spreads to the appropriate l atitudes, and these structured westward currents are observed in areas where the UV auroral luminosity is high. Justifications that the calc ulated equivalent currents are real ionospheric currents are presented . Calculation of the ionospheric conductivity based on the measurement s of precipitating electrons from DMSP-F7 shows that the conductivity in the regions of the westward filaments is enhanced.