Occurrence frequency and location of magnetic islands at the dayside magnetopause

Abstract

Simulations of magnetic reconnection often predict the formation of magnetic islands forming and propagating out through the reconnection exhaust region. However, to date, only a few observations of magnetic islands at the Earth's magnetopause have been identified and analyzed. Crossings near reconnection sites at the dayside magnetopause by Cluster from 2001 to 2009 are examined in a systematic effort to determine the frequency and location of magnetic islands. Using the maximum magnetic shear model as a guide for the distance to the reconnection site, 47 magnetopause crossings within 3 RE of the predicted reconnection site are examined. The occurrence of island structures in the reconnection exhaust is investigated in the context of how the type of reconnection, antiparallel or component, affects the frequency of formation of the islands. For Cluster magnetopause crossings confirmed to be near reconnection sites, island signatures, primarily bidirectional streaming electrons in the magnetosheath boundary layer, are seen for approximately 85% of the crossings and are common features for both antiparallel and component reconnection.