Dayside auroral activity and magnetospheric boundary layer phenomena.

Abstract

Selected case studies of auroral structure/activity observed at different local times on the dayside are presented and discussed in the context of electrodynamic coupling between the different magnetospheric boundary regions and the ionosphere. The first case addresses the question of the auroral signatures of the two boundary regions referred to as cusp and cleft/LLBL. Combined ground-based and satellite data reveal the different latitudinal zones of auroral forms/particle precipitation/field-aligned current and the relationship with the respective magnetospheric plasma populations, i. e. CPS, BPS, LLBL, and the plasma mantle. Midday auroral breakup events and the related ionospheric ion drift and magnetic observations show many of the features that have been predicted to be ionospheric signatures of flux transfer events. An alternative explanation that has been proposed by others, i. e. ionospheric effect of magnetopause perturbations excited by dynamic pressure pulses in the magnetosheath is also discussed. A critical question in this respect is the location of the breakup event sequence in relation to the polar cap boundary. Does the poleward motion of the events correspond to newly-reconnected flux tubes moving into the polar cap or to an outward radial motion of the magnetopause and the boundary layers, associated with changes in the external dynamic pressure? Periodic auroral forms in the 14-15MLT sector, within 70-70° MLAT, and associated Pc5 magnetic pulsations at lower latitudes are discussed in terms of large-scale waves on the LLBL/PS interface.