Magnetic island formation between large‐scale flow vortices at an undulating postnoon magnetopause for northward interplanetary magnetic field

Abstract

Time History of Events and Macroscale Interactions during Substorms multispacecraft observations are presented for a ∼2‐h‐long postnoon magnetopause event on 8 June 2007 that for the first time indicate that the trailing (sunward) edges of Kelvin‐Helmholtz (KH) waves are commonly related to small‐scale <0.56 RE magnetic islands or flux transfer events (FTE) during the growth phase of these surface waves. The FTEs typically show a characteristic bipolar BN structure with enhanced total pressure at their center. Most of the small‐scale FTEs are not related to any major plasma acceleration. TH‐A observations of one small FTE at a transition from the low‐latitude boundary layer (LLBL) into a magnetosheath plasma depletion layer were reconstructed using separate techniques that together confirm the presence of a magnetic island within the LLBL adjacent to the magnetopause. The island was associated with a small plasma vortex and both features appeared between two large‐scale (∼1 RE long and 2000 km wide) plasma vortices. We propose that the observed magnetic islands may have been generated from a time‐varying reconnection process in a low ion plasma beta (βi < 0.2) and low 8.3° field shear environment at the sunward edge of the growing KH waves where the local magnetopause current sheet may be compressed by the converging flow of the large‐scale plasma vortices as suggested by numerical simulations of the KH instability.