The auroral distribution and its relation to magnetospheric processes

Abstract

The auroral distribution has several aspects which can be naturally related to magnetospheric processes. Dayside asymmetries in intensity and location of emissions enable one to visualize the implied convection and thus the geometry of dayside boundary regions. For B y > 0 (B y < 0) northern hemisphere polar arcs tend to be confined to the dusk (dawn) sector and the dusk (dawn) auroral distribution tends to lie poleward of the dawn (dusk) emissions near noon. These observations are consistent with the orientation of the convection throat and its dependence on IMF B y. High latitude dayside features, poleward of the particle cusp, are also dependent on B y and confirm that there is indeed a separate auroral system (and presumably current system) in the particle plasma mantle region (as defined by DMSP). The distribution of the auroras in the midnight sector during both quiet and disturbed times allows one to make important inferences about the mapping of these forms into the magnetotail. Fundamental to this is the observations of a continuous oval throughout the night sector, the location of substorm onset relative to this oval and the subsequent development of a “double oval” during substorm recovery. A unique set of observations are given illustrating how the different portions of the “double oval” develop during a substorm expansion phase. These observations support the view that on some occasions the expansion phase dominantly affects the central plasma sheet and leaves the inner and outer edges of the magnetotail relatively undisturbed. New observations concerning the dynamics of arc development westward of the auroral surge supports an hypothesis of Alfven waves modulating currents which in turn give rise to magnetic pulsations and multiple auroral arc systems.