Strongly localized magnetic reconnection by the super-Alfvenic shear flow

TL;DR

This paper reveals that super-Alfvenic shear flows can strongly localize magnetic reconnection in collisionless plasmas, enabling a new morphology driven by electron inertia, with a reconnection rate remaining around 0.1.

Contribution

It introduces a novel reconnection morphology caused by super-Alfvenic shear flows, distinct from resistive-MHD, and explains the persistent fast reconnection rate.

Findings

Magnetic field dragging by shear flows localizes the reconnection x-line.

Reconnection rate remains ~0.1 despite large x-line aspect ratio.

Localization mechanism is not solely due to tearing modes.

Abstract

We demonstrate the dragging of the magnetic field by the super-Alfvenic shear flows out of the reconnection plane can strongly localize the reconnection x-line in collisionless plasmas, reversing the current direction at the x-line. Reconnection with this new morphology, which is impossible in resistive-magnetohydrodynamic (MHD), is enabled by electron inertia. Surprisingly, the quasi-steady reconnection rate remains of order 0.1 even though the aspect ratio of the local x-line geometry is larger than unity. We explain this by examining the transport of the reconnected magnetic flux and the opening angle made by the upstream magnetic field, concluding that the reconnection rate is still limited by the constraint imposed at the inflow region. This study further suggests the nearly universal fast rate value of order 0.1 cannot be explained by the physics of tearing modes, nor can it be explained by a universal localization mechanism.