Large — and Small — Scale Dynamics of the Polar Cusp Region

Abstract

Photometric observations from two stations on Svalbard, Norway, have been used to map the location and dynamics of polar cusp auroras. Cases showing the behaviour of cusp auroras and the local magnetic field related to changes in the interplanetary magnetic field (IMF) and irregularities in the solar wind plasma are presented. Dynamical phenomena with different time scales are studied. South- and northward expansions of the midday sector of the auroral oval are connected with south- and northward turnings of the IMF, measured just outside the bow-shock (ISEE-1 data). No direct relationship to substorm activity was observed. Intensifications and rapid motions of discrete auroral structures in the cusp region are shown to be associated with local Pi-type magnetic pulsations, each event lasting a few minutes. These small-scale dynamical phenomena are discussed in relation to the concept of impulsive penetration of plasma irregularities across the dayside magnetopause, from the magnetosheath to the polar cusp region of the magnetosphere.