Magnetic Reconnection in Two-Dimensional Magnetohydrodynamic Turbulence

Abstract

Systematic analysis of numerical simulations of two-dimensional magnetohydrodynamic turbulence reveals the presence of a large number of X-type neutral points where magnetic reconnection occurs. We examine the statistical properties of this ensemble of reconnection events that are spontaneously generated by turbulence. The associated reconnection rates are distributed over a wide range of values and scales with the geometry of the diffusion region. Locally, these events can be described through a variant of the Sweet-Parker model, in which the parameters are externally controlled by turbulence. This new perspective on reconnection is relevant in space and astrophysical contexts, where plasma is generally in a fully turbulent regime.

Response to “Comment on ‘Scaling of asymmetric magnetic reconnection: General theory and collisional simulations’ ” [Phys. Plasmas 16, 034701 (2009)]

“…Our own simulations confirmed these results for Sweet-Parker reconnection in resistive magnetohydrodynamics ͑MHD͒ simulations for asymmetric fields 1 and asymmetric densities 3 and for Hall reconnection in two-fluid ͑Hall-MHD with electron inertia͒ simulations for all combinations of asymmetries. 4 In addition, the reconnection rate E ͑whose derivation depends on the relation in question͒ has been confirmed by simulations from other groups [5][6][7][8][9] in various settings using various simulation techniques.…”

Role of Z-pinches in magnetic reconnection in space plasmas

“…Alternative scenarios of magnetic reconnection in turbulent plasmas were proposed by Che et al (2011);Daughton et al (2011) based on numerical simulations with topologies resembling X-lines. Recently emerging is a scenario of reconnection in turbulence, reported in MHD (Servidio et al 2009), PIC (Karimabadi et al 2013b) simulations, and in solar wind measurements (Osman et al 2014). However, the major question remains unanswered: could these reconnection scenarios produce the observed high dissipation rates of magnetic field energy, or there are other mechanisms?…”

On the accuracy of simulations of turbulence

“…We also examine the performance of these simple tests in the context of a magnetohydrodynamics ͑MHD͒ problem that is very demanding in terms of spatial resolution, namely, the determination of rates of magnetic reconnection in turbulence. 6,7 In much of the literature involving simulations of hydrodynamic turbulence, a numerical aim is to attain the highest possible Reynolds numbers so that the properties of fully developed or strong turbulence can be studied. This is often motivated by efforts to understand natural systems that have very high Reynolds number flows, or else to examine theoretical issues that pertain to the asymptotic limit of high Reynolds number, where certain universal features may obtain.…”