About the relative importance of compressional heating and current dissipation for the formation of coronal X-ray Bright Points

TL;DR

This study uses 3D resistive MHD simulations based on observed magnetic fields to analyze the energy contributions of compression and current dissipation in forming coronal X-ray bright points, highlighting the dominance of adiabatic compression over Joule heating.

Contribution

It demonstrates that adiabatic compression plays a more significant role than current dissipation in coronal bright point formation, challenging assumptions about the dominance of Joule heating in such processes.

Findings

Adiabatic compression significantly increases thermal energy in coronal bright points.

Joule heating has a minor effect compared to pressure-driven compression.

High resistivity in models can produce unphysical energy balance results.

Abstract

Context. The solar corona is heated to high temperatures of the order of 10^{6} K. The coronal energy budget and specifically possible mechanisms of coronal heating (wave, DC-electric fields, ..) are poorly understood. This is particularly true as far as the formation of X-ray bright points (BPs) is concerned. Aims. Investigation of the energy budget with emphasis on the relative role and contribution of adiabatic compression versus current dissipation to the formation of coronal BPs. Methods. Three-dimensional resistive MHD simulation starts with the extrapolation of the observed magnetic field from SOHO/MDI magnetograms, which are associated with a BP observed on 19 December 2006 by Hinode. The initial radially non-uniform plasma density and temperature distribution is in accordance with an equilibrium model of chromosphere and corona. The plasma motion is included in the model as a source of energy for coronal heating. Results. Investigation of the energy conversion due to Lorentz force, pressure gradient force and Ohmic current dissipation for this bright point shows the minor effect of Joule heating in comparison to the work done by pressure gradient force in increasing the thermal energy by adiabatic compression. Especially at the time when the temperature enhancement above the bright point starts to form, compressional effects are quite dominant over the direct Joule heating. Conclusions. Choosing non-realistic high resistivity in compressible MHD models for simulation of solar corona can lead to unphysical consequences for the energy balance analysis, especially when local thermal energy enhancements are being considered.