Magnetic reconnection in strongly magnetized regions of the low solar chromosphere

TL;DR

This study uses advanced MHD simulations to explore magnetic reconnection in the low solar chromosphere, revealing the importance of non-equilibrium ionization dynamics and their effects on reconnection rates and plasma heating.

Contribution

It demonstrates the critical role of non-equilibrium ionization-recombination processes in magnetic reconnection in the low solar atmosphere, a novel insight for partially ionized plasma modeling.

Findings

Non-equilibrium ionization affects reconnection structure and temperature.

Reconnection rate is faster with non-equilibrium ionization.

Weakly ionized plasma can become fully ionized and heated during reconnection.

Abstract

Magnetic reconnection in strongly magnetized regions around the temperature minimum region of the low solar atmosphere is studied by employing MHD-based simulations of a partially ionized plasma within a reactive 2.5D multi-fluid model. It is shown that in the absence of magnetic nulls in a low $\beta$ plasma the ionized and neutral fluid flows are well-coupled throughout the reconnection region. However, non-equilibrium ionization-recombination dynamics play a critical role in determining the structure of the reconnection region, lead to much lower temperature increases and a faster magnetic reconnection rate as compared to simulations that assume plasma to be in ionization-recombination equilibrium. The rate of ionization of the neutral component of the plasma is always faster than recombination within the current sheet region even when the initial plasma $\beta$ is as high as $\beta_0=1.46$. When the reconnecting magnetic field is in excess of a kilogauss and the plasma $\beta$ is lower than 0.0145, the initially weakly ionized plasmas can become fully ionized within the reconnection region and the current sheet can be strongly heated to above $2.5\times10^4$~K, even as most of the collisionally dissipated magnetic energy is radiated away. The Hall effect increases the reconnection rate slightly, but in the absence of magnetic nulls it does not result in significant asymmetries or change the characteristics of the reconnection current sheet down to meter scales.