Numerical Studies of Weakly Stochastic Magnetic Reconnection

TL;DR

This study uses 3D numerical simulations to test a model of fast magnetic reconnection influenced by turbulence, confirming the model's predictions and elucidating how turbulence parameters affect reconnection rates.

Contribution

First numerical validation of the Lazarian & Vishniac (1999) model showing turbulence enhances reconnection speed and alters magnetic topology.

Findings

Reconnection speed scales as V^2 with turbulence velocity amplitude.

Reconnection rate depends on injection scale as (l/L)^(2/3).

Global reconnection rate is independent of resistivity in turbulent conditions.

Abstract

We study the effects of turbulence on magnetic reconnection using three-dimensional numerical simulations. This is the first attempt to test a model of fast magnetic reconnection proposed by Lazarian & Vishniac (1999), which assumes the presence of weak, small-scale magnetic field structure near the current sheet. This affects the rate of reconnection by reducing the transverse scale for reconnection flows and by allowing many independent flux reconnection events to occur simultaneously. We performed a number of simulations to test the dependencies of the reconnection speed, defined as the ratio of the inflow velocity to the Alfven speed, on the turbulence power, the injection scale and resistivity. Our results show that turbulence significantly affects the topology of magnetic field near the diffusion region and increases the thickness of the outflow region. We confirm the predictions of the Lazarian & Vishniac model. In particular, we report the growth of the reconnection speed proportional to ~ V^2, where V is the amplitude of velocity at the injection scale. It depends on the injection scale l as ~ (l/L)^(2/3), where L is the size of the system, which is somewhat faster but still roughly consistent with the theoretical expectations. We also show that for 3D reconnection the Ohmic resistivity is important in the local reconnection events only, and the global reconnection rate in the presence of turbulence does not depend on it.