Reconnection at the dayside magnetopause: Comparisons of global MHD simulation results with Cluster and Double Star observations

Abstract

This study uses two conjunctions between Cluster and Double Star TC‐1 spacecraft together with global magnetohydrodynamic (MHD) simulations to investigate the large‐scale configuration of magnetic reconnection at the dayside magnetopause. Both events involve southward interplanetary magnetic fields with significant By components. The first event occurred on 8 May 2004, while both spacecraft were exploring the dawn flank of the magnetosphere; TC‐1 was skimming the magnetopause whereas Cluster was exploring higher latitudes. Results from a global MHD simulation show the formation of an equatorial merging line in the morning sector and suggest that the three‐dimensional geometry of the merging region is mostly a radial juxtaposition of planes displaying X‐type reconnection geometries. The second conjunction was on 6 April 2004. During this event, Cluster was located at high latitudes and close to the noon‐midnight meridian, while TC‐1 was exploring the dawnside at low latitudes. Analysis of the simulation reveals that both antiparallel and component merging occurred simultaneously. Three‐dimensional rendering of the parallel electric field indicates that component merging initiated in the subsolar magnetopause. Simulation runs carried out using different parameters in the model suggest that the spread of the merging region depends on the local resistivity. The subsolar‐merging region grows with increasing resistivity values and becomes patchy when a resistivity threshold is used. However, the region of component merging appears to remain spatially constrained to the subsolar region where stronger parallel electric fields occur and no clear connection with the antiparallel‐merging regions is found for the range of parameters surveyed.