Auroral Signatures of Magnetospheric Substorms and Constraints which They Provide for Substorm Theories

Abstract

Magnetospheric substorms reflect the most pronounced periods of energy transfer from the solar wind to the magnetosphere and ionosphere of the Earth. Modern views of the substorm process have been substantially modified in the past few years by information inferred from analysis and interpretation of auroral images acquired by the UV imager flown aboard the Viking satellite. In this paper, I shall summarize some of the findings from the ongoing study of the Viking data base dealing with the nature of auroral surges in the evening sector and omega bands in the morning sector. These auroral forms reflect the growth of instabilities in the magnetosphere-ionosphere system and provide important information on the properties of the geospace environment in which the free energy to drive the instabilities is found. Substorms were originally defined using ground based arrays of detectors and any theory of substorms must account for the temporal and spatial properties of auroral forms. Any theory that does not address these questions is incomplete. The information presented in this paper therefore provides constraints which are necessary to incorporate into any theory of magnetospheric substorms.