Authors: Mehmet Sarp Yalim (University of Alabama in Huntsville), Sanjiv Tiwari (Bay Area Environmental Research Institute), Debi Prasad Choudhary (California State University, Northridge), Christian Beck (National Solar Observatory), Sushree Nayak (University of Alabama in Huntsville), Madison Drake (University of Alabama in Huntsville)

The physics of the solar chromosphere is complex from both theoretical and modeling perspectives. The plasma temperature from the photosphere to corona increases from 5,000 K to ~1 million K over a distance of only 10,000 km in the chromosphere and transition region. Understanding the mechanisms underlying the heating of the solar atmosphere is a fundamental problem in solar physics. We investigate Joule heating as a solar active region atmosphere heating mechanism, in particular in the lower chromosphere where Cowling resistivity is dominant, resulting from the anisotropic dissipation of electric currents parallel and perpendicular to the magnetic field by Coulomb and Cowling resistivities, respectively due to the weakly-ionized plasma environment. We focus on target structures where strong gradients in the magnetic field strength and field orientation are prevalent resulting in currents such as light bridges inside the umbra of sunspots, magnetic flux emergence into a field-free or magnetic environment, polarity inversion lines or magnetic reconnection sites like Ellerman bombs. To calculate the Cowling resistivity and the resulting Joule heating rate which we call Cowling heating, we developed a state-of-the-art data-constrained analysis based on observational data from space-based and ground-based solar observational instruments as well as tabulated data from theoretical or semi-empirical solar atmosphere models. We previously showed that Cowling heating is a dominant heating mechanism for an umbral sunspot light bridge. In this study, we present our analysis on a second umbral light bridge that we also confirmed to be primarily heated by this mechanism by incorporating magnetic field data from SDO/HMI vector magnetograms, and temperature data from IRIS obtained from inversions of spectroscopic data into our analysis. This investigation, supported by an NSF SHINE award, will be an important contribution to the existing efforts on chromospheric heating research.