Mapping of the auroral oval and individual arcs during substorms

Abstract

Magnetospheric mappings of the auroral oval during the course of a substorm are presented for an event where conjugate auroral imaging was available (CDAW 9 event C on May 3, 1986). The mappings have been computed using time‐evolving magnetic field models developed for the substorm 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 the substorm recovery phase maps mostly within the lunar distance. The void (weak luminosity) regions between the poleward and equatorward arc systems are connected to the region 20–30 RE down the tail. To complement the global view, mappings of individual growth phase auroral arcs were undertaken. These mappings did not result in a coherent pattern, suggesting that these arcs may be formed by low‐altitude acceleration region processes rather than plasma sheet instabilities.