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

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 the magnetic island coalescence problem under two interesting scenarios. First, 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 of the islands increases, resulting in an increase in upstream magnetic field, upstream velocity field, and unnormalized reconnection rate. However, the downstream magnetic field, current sheet length and normalized reconnection rate (normalized to the upstream magnetic field and upstream Alfvénic velocity) remain independent of it. Interestingly, the reconnection rate is found to be different from the upstream to downstream velocity ratio as well as from the aspect ratio of the current sheet, as opposed to the findings of the Sweet–Parker model. Second, 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, and the differences are more in stronger shear flows. These results are significantly different from the Harris sheet setup with shear flow.