Asymmetric Magnetic Reconnection in Weakly Ionized Chromospheric Plasmas

TL;DR

This paper presents 2.5D simulations of asymmetric magnetic reconnection in the partially ionized solar chromosphere, revealing how plasma and neutral components behave differently under asymmetric conditions and the influence of Hall effects.

Contribution

It introduces detailed simulations of asymmetric reconnection in weakly ionized plasmas, accounting for non-equilibrium ionization and plasma-neutral decoupling, which were not previously modeled.

Findings

Neutrals flow from weak to strong magnetic field regions due to pressure gradients.

Hall effect modifies magnetic field structures but does not produce typical X-point geometry.

Plasmoids form after initial laminar reconnection phase.

Abstract

Realistic models of magnetic reconnection in the solar chromosphere must take into account that the plasma is partially ionized and that plasma conditions within any two magnetic flux bundles undergoing reconnection may not be the same. Asymmetric reconnection in the chromosphere may occur when newly emerged flux interacts with pre-existing, overlying flux. We present 2.5D simulations of asymmetric reconnection in weakly ionized, reacting plasmas where the magnetic field strengths, ion and neutral densities, and temperatures are different in each upstream region. The plasma and neutral components are evolved separately to allow non-equilibrium ionization. As in previous simulations of chromospheric reconnection, the current sheet thins to the scale of the neutral-ion mean free path and the ion and neutral outflows are strongly coupled. However, the ion and neutral inflows are asymmetrically decoupled. In cases with magnetic asymmetry, a net flow of neutrals through the current sheet from the weak field (high density) upstream region into the strong field upstream region results from a neutral pressure gradient. Consequently, neutrals dragged along with the outflow are more likely to originate from the weak field region. The Hall effect leads to the development of a characteristic quadrupole magnetic field modified by asymmetry, but the X-point geometry expected during Hall reconnection does not occur. All simulations show the development of plasmoids after an initial laminar phase.