The Enhancement of Ion Heating in Kinetic, Anti-Parallel Reconnection in the Presence of a Flow Shear

Abstract

We investigate the kinetic effects of upstream, magnetic field-aligned, flow shear on anti-parallel magnetic reconnection using 2.5D Particle-In-Cell simulations. Our results demonstrate that flow shear significantly alters the reconnection process, leading to enhanced ion heating, reduced outflow speeds, and a modified reconnection geometry. In contrast to previous Hall Magnetohydrodynaic (MHD) studies, we find that reconnection becomes a more efficient plasma heating mechanism in the presence of sub-Alfv\'enic flow shear, with ion heating increasing by as much as 300\%. This enhanced heating is achieved by efficiently converting the incoming flow shear energy into thermal energy through istropization in the exhaust. The enhanced heating leads to a pressure gradient away form the x-line exerting a force that reduces the outflow jet speed and slows down the reconnection process. This conversion is due to beam selection effects, mixing and scattering in the exhaust. A theoretical model is developed which predicts well the exhaust heating and outflow speed reduction. These results offer a potential explanation for recent Parker Solar Probe observations of suppressed reconnection in the presence of flow shear and carry significant implications for energy dissipation in turbulent plasmas.