Dayside aurora and relevance to substorm current systems and dayside merging

Abstract

Photometric keograms from South Pole Station are used to investigate dayside auroral precipitation. Identification of cusp auroral signatures allows cusp movements to be monitored and correlated with substorm activity and interplanetary magnetic field direction. We conclude that any erosion of dayside field is not a direct result of southward turning B z . On the other hand, cusp position is intimately related to substorm timing and intensity. We suggest the associated dayside field reconfiguration results from diversion of near‐tail magnetopause currents through the nightside electrojet because of enhanced auroral ionosphere conductivity. This interpretation implies that substorms result from increased efficiency of the extraction of energy from the solar wind rather than from a release of internally stored magnetic energy in the tail.