Scaling of reconnection parameters in magnetic island coalescence: Role of in-plane shear flow

TL;DR

This study investigates how magnetic island size and in-plane shear flow influence reconnection parameters in 2D viscoresistive-MHD models, revealing new scaling behaviors and differences from classical models with implications for space and fusion plasmas.

Contribution

It provides novel insights into the scaling of reconnection parameters with island size and shear flow effects, contrasting with traditional models like Sweet-Parker and Harris sheet setups.

Findings

Reconnection rate remains independent of island width when normalized.

Shear flow significantly alters current sheet inclination and diffusion region.

Differences observed between current sheet inclination and diffusion region angles.

Abstract

A 2D incompressible viscoresistive-MHD model [Mahapatra et. al., Phys. Plasmas 28, 072103 (2021)] is used to study the scaling of reconnection parameters in magnetic island coalescence problem under two interesting scenarios. Firstly, the effect of changing island half-width at a fixed system size is investigated. As the island half-width increases, the total magnetic flux content increases resulting in an increase in upstream magnetic field, upstream velocity field and unnormalized reconnection rate while keeping the normalized rate, downstream magnetic field and current sheet length independent of it. Interestingly, the reconnection rate is found to be different from the upstream and downstream velocity as well as inverse aspect ratio of the current sheet, as opposed to the findings of the Sweet-Parker model. Secondly, the in-plane shear flow effects are studied, keeping the island width and system size fixed. Here thickness and length of the current sheet, the upstream magnetic and velocity field components, reconnection rate and time, current sheet inclination angle with shear flow length scale and amplitude are calculated. Interestingly, the inclination angle of the current sheet and the diffusion region are found to be different. These differences are more in stronger shear flows. These results are significantly different from the Harris sheet setup with shear flow. The results have potential application in the Earth magnetospheric observations and fusion plasma experiments.