MAPPING OF THE AURORAL OVAL AND INDIVIDUAL ARCS DURING SUBSTORMS

Magnetospheric mappings of the auroral oval during the course of a sub storm are presented for an event where conjugate auroral imaging was a vailable (CDAW 9 event C on May 3, 1986). The mappings have been compu ted using time-evolving magnetic field models developed for the substo rm growth and recovery phases. We show that even though the models do not contain field-aligned currents, conjugacy between images from the two hemispheres is good. Furthermore, the high time resolution Viking images show an accurate comparison with the east-west spreading of the substorm current wedge observed by four spacecraft in the near-Earth tail. We also show that the double oval configuration present during t he substorm recovery phase maps mostly within the lunar distance. The void (weak luminosity) regions between the poleward and equatorward ar e systems are connected to the region 20-30 R(E) down the tail. To com plement the global view, mappings of individual growth phase auroral a rcs were undertaken. These mappings did not result in a coherent patte rn, suggesting that these arcs may be formed by low-altitude accelerat ion region processes rather than plasma sheet instabilities.