Evolution of an MHD-scale Kelvin-Helmholtz vortex accompanied by magnetic reconnection: Two-dimensional particle simulations

Abstract

We have performed 2.5-dimensional full particle simulations of an MHD-scale Kelvin-Helmholtz (KH) vortex and accompanying magnetic reconnection. This is the first study of so-called vortex-induced reconnection (VIR) using kinetic simulations. First, as a key property of the VIR, we found that magnetic reconnection occurs at multiple points in the current sheet compressed by the flow of the KH vortex. The resulting multiple mesoscale islands are carried toward the vortex body along the vortex flow and then are incorporated into the vortex body via re-reconnection. The rates of the first reconnection and second re-reconnection are both generally higher than that of spontaneous reconnection; both reconnection processes are of driven nature. Noteworthy is that the high rate of the first reconnection leads to strong magnetic field pileup within the multiple islands. This characteristic magnetic structure of the islands could be used as new observational evidence for the occurrence of the VIR. Next, as a key kinetic aspect of the VIR, we found that a series of the multiple island formation and incorporation processes causes efficient plasma mixing in real space and bidirectional magnetic field-aligned acceleration of electrons simultaneously within the vortex. These kinetic effects of the VIR could account for observed features of the Earth's low-latitude boundary layer, where mixed ions and bidirectional field-aligned electrons generally coexist.