Turbulent reconnection of magnetic bipoles in stratified turbulence

TL;DR

This study investigates magnetic reconnection in stratified turbulence, revealing that bipolar magnetic structures form near the surface and reconnection rates become independent of Lundquist number at high values, aligning with recent simulation results.

Contribution

It provides a systematic numerical analysis of magnetic reconnection in stratified turbulence, highlighting the formation of bipolar structures and their reconnection behavior at high Lundquist numbers.

Findings

Bipolar magnetic structures form near the surface in stratified turbulence.

Reconnection rate becomes independent of Lundquist number for S > 10^3.

Formation of elongated bipolar bands with sharp polarity interfaces.

Abstract

We consider strongly stratified forced turbulence in a plane-parallel layer with helicity and corresponding large-scale dynamo action in the lower part and non-helical turbulence in the upper. The magnetic field is found to develop strongly concentrated bipolar structures near the surface. They form elongated bands with a sharp interface between opposite polarities. Unlike earlier experiments with imposed magnetic field, the inclusion of rotation does not strongly suppress the formation of these structures. We perform a systematic numerical study of this phenomenon by varying magnetic Reynolds number, scale separation ratio, and Coriolis number. We focus on the formation of a current sheet between bipolar regions where reconnection of oppositely oriented field lines occurs. We determine the reconnection rate by measuring either the inflow velocity in the vicinity of the current sheet or by measuring the electric field in the reconnection region. We demonstrate that for large Lundquist numbers, S>10^3, the reconnection rate is nearly independent of S in agreement with results of recent numerical simulations performed by other groups in simpler settings.