Implications of Viking imager results for substorm models

Abstract

Ultraviolet auroral images obtained with the Viking satellite are used in conjunction with other data sets and magnetospheric magnetic modelling tools to provide new observations of expansion phase dynamics and to evaluate the major substorm models. Towards this end, a statistical survey of Viking optical onsets is performed. The short-term development of auroral forms within the bulge during the expansion phase are described and compared with geosyncronous particle data. It is found that intensifications of the poleward arc are an important means by which the poleward expansion of the bulge occurs. Such intensifications can lead to the formation of north-south aligned forms and particle injections at geosyncronous orbit. Various mapping techniques were used to infer magnetospheric source locations of substorms. The results generally point to a near earth location for onset. In addition, observations of the activation of auroral forms in the dusk sector suggest that the low latitude boundary layer becomes an active component during the expansion phase. Thus, substorms involve both internal magnetospheric processes as well as boundary layer processes. The implications of these and other Viking imager results are discussed.