Dayside polar cusp/cleft aurora: Morphology and dynamics

Abstract

Observations of auroral forms and activities occurring at daytime cusp latitudes and their correspondence with ionospheric convection structures, magnetic deflections, particle precipitation, solar wind and IMF conditions are reported. The different dayside auroral forms may be sorted according to magnetic field configuration (open versus closed), magnetospheric plasma source region and upstream (solar wind/IMF) conditions. Two major cusp auroral forms occur at different latitudes corresponding to different IMF orientations and ionospheric convection configurations. Transitions from one form to the other are often observed in association with IMF directional discontinuities involving B Z polarity changes. It is suggested that the auroral forms located at lower and higher latitudes correspond to plasma injections associated with magnetic reconnections at low and high magnetopause latitudes, respectively. Special attention is placed on the phenomenon of poleward-moving auroral forms at cusp/mantle latitudes and its possible association with pulsed reconnection at low magnetopause latitudes.