Solar wind interaction with the Earth's magnetosphere: the role of reconnection in the presence of a large scale sheared flow

Abstract

Abstract. The Earth's magnetosphere and solar wind environment is a laboratory of excellence for the study of the physics of collisionless magnetic reconnection. At low latitude magnetopause, magnetic reconnection develops as a secondary instability due to the stretching of magnetic field lines advected by large scale Kelvin-Helmholtz vortices. In particular, reconnection takes place in the sheared magnetic layer that forms between adjacent vortices during vortex pairing. The process generates magnetic islands with typical size of the order of the ion inertial length, much smaller than the MHD scale of the vortices and much larger than the electron inertial length. The process of reconnection and island formation sets up spontaneously, without any need for special boundary conditions or initial conditions, and independently of the initial in-plane magnetic field topology, whether homogeneous or sheared.

A case study of Kelvin–Helmholtz vortices on both flanks of the Earth's magnetotail

“…In particular, secondary instabilities excited in the vortices have been proposed as candidates for transport of the SW plasma into the magnetosphere (e.g. Matsumoto and Hoshino, 2004;Califano et al, 2009).…”

Collisionless magnetic reconnection in the presence of a sheared velocity field

“…In that case, the reconnection occurring during the development of the Kelvin-Helmholtz instability is thus driven by the faster ideal instability. [18][19][20][21][22] APPENDIX: SLOW GROWTH REGIME Let us consider the slow growth regime, where ␥ / ␣FЈ͑0͒⑀ Ӷ 1, in the "comparable shear" regime, where ͉GЈ͑0͉͒ / FЈ͑0͒ϳ1. For the sake of simplicity, we take…”

“…Furthermore, it has been shown that the velocity field, generated by Kelvin-Helmholtz instability, is able to force the magnetic field lines to reconnect. [18][19][20][21][22] This reconnection is not an instability but is induced by the ideal Kelvin-Helmholtz instability. In fact, for a resistive plasma, the rate at which it happens is independent from the value of the resistivity and is related only to the Kelvin-Helmholtz growth rate.…”

“…If the magnetic field has an inversion line ͓we refer, for simplicity, to a two-dimensional ͑2-D͒ configuration, see below͔, the fluid velocity field, modified by the linear evolution of Kelvin-Helmholtz, forces the magnetic lines to reconnect and to follow the evolution imposed by the Kelvin-Helmholtz instability. [18][19][20][21][22] On the contrary, if the magnetic field initially has no inversion line, magnetic reconnection cannot occur during the linear phase of the KelvinHelmholtz instability. However, the nonlinear evolution of the Kelvin-Helmholtz vortices is able to roll up and stretch the magnetic lines, producing inversion regions and leading to the formation of reconnection unstable current layers.…”

“…In this case, reconnection is not an instability but is simply driven by the far faster ideal instability. [18][19][20][21][22] …”