Viking observations of the UV dayside aurora and their relationship to DMSP particle boundary definitions

Abstract

Viking images of the dayside auroral distribution have been used in conjunction with DMSP-F7 satellite particle data to intercalibrate the two data sets. As a result of the Geospace Environmental Modelling Program, an effort has been made to determine where the dayside aurora occurs relative to the various particle regions defined by means of a neural network. In general, the main dayside auroral emissions in the wavelength regime 1400-1800 A are continuous between 8 and 16 MLT. Sometimes, however, a noon sector gap can be seen, which is associated with an auroral distribution in which the dusk and dawn sector auroral regions occur at different latitudes (resembling overlapping convection cells). It is not, in general, correct to make a one-to-one correspondence between this gap and the cusp defined by DMSP particle data. The normal dayside aurora appears to be a manifestation of the central and boundary plasma sheet (CPS, BPS) and Low Latitude Boundary Layer (LLBL) particle signatures, with the DMSP cusp particle signature observed just poleward of this. If the mid-day region of weak UV auroral intensity is a signature of the convection throat signature is not always coincident with the DMSP particle cusp location. In addition to the stable auroral oval there are auroral signatures consistent with the particle definition of the poleward edge of the plasma mantle or start of the polar rain. These auroral forms are probably the two-dimensional ionospheric signature of the cusp/mantle current system and as such contain valuable information concerning the dynamics and large scale structure of that system