A Data-constrained Analysis for Joule Heating as a Solar Active Region Atmosphere Heating Mechanism. I. Sunspot Umbral Light Bridge

Abstract

Understanding the mechanisms underlying the heating of the solar atmosphere is a fundamental problem in solar physics. The lower atmosphere of the Sun (i.e., photosphere and chromosphere) is composed of weakly ionized plasma. This results in anisotropic dissipation of electric currents by Coulomb and Cowling resistivities. Joule heating due to dissipation of currents perpendicular to the magnetic field by Cowling resistivity has been demonstrated to be the main mechanism for the heating of a sunspot umbral light bridge located in NOAA AR 12002 on 2014 March 13. Here, we focus on the same target region and demonstrate the importance of further constraining our Joule heating model using observational data in addition to magnetic field, namely plasma temperature calculated from the inversion of spectroscopic data obtained from the Interferometric BI-dimensional Spectrometer instrument of the ground-based Dunn Solar Telescope. As a parameter in our analysis, temperature is demonstrated to have the highest sensitivity after magnetic field. We show that the heating of the light bridge is a highly dynamic event that necessitates utilization of 3D spatially resolved observational data for temperature rather than a 1D temperature stratification based on theoretical/semiempirical solar atmosphere models. Our improved data-constrained analysis using spatially resolved temperatures shows that the entire light bridge is heated by the proposed mechanism, and yields heating rate values that are consistent with our previous study.

Keywords

• Solar chromosphere
• Solar chromospheric heating
• Solar active region magnetic fields