Electron signatures of active merging sites on the magnetopause

Abstract

Near magnetopause current layers the Polar satellite often detects field-aligned fluxes of >0.5 keV electrons that carry heat flux away from merging sites along inner/outer separatrices between newly opened and closed/interplanetary magnetic flux. Close to separator lines, electron gyrotropy weakens to break trapping on closed field lines of the outer plasma sheet followed by attachment to newly opened flux at random pitch angles. Energetic electrons in the "tails" of distribution functions quickly move great distances along separatrices to act as surgical indicators of active merging. If IMF BY is large, field rotation in the magnetopause current layer can be ≪ 180°, obscuring relationships between merging sources and separatrices. Suprathermal electrons and accelerated ions moving along nearby inner and outer edges of moderate shear current layers are remote signatures of merging at widely separate locations. Detecting accelerated ions at a moderate shear magnetopause is insufficient evidence for component merging occurring near a spacecraft. During magnetopause-skimming passes Polar sampled electron tail events characteristic of inner and outer separatrices that typically lasted from a few tens of seconds to several minutes. The 557.7-nm emissions observed at cusp boundaries suggest that their sources operate on similar timescales and are active simultaneously at multiple locations. The magnetic conjugacy of inner separatrices with cusp boundaries as well as the similar timescales of electron tail and 557.7-nm emission events strongly indicates that they are causally connected. Combining the two types of measurements offers an effective technique for separating temporal and spatial variability in magnetopause dynamics. Copyright 2005 by the American Geophysical Union.