SHINE: Joule Heating as a Solar Active Region Atmosphere Heating Mechanism

University Of Alabama In Huntsville, Huntsville AL

Investigators

Abstract

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. How this happens is the biggest mystery in solar physics today. This project investigates this process through an observational study of several NSF and NASA data sets. The work supports early career scientists, including a female post-doctoral researcher and REU students. This project is jointly funded by the Solar-Terrestrial Research program and the Established Program to Stimulate Competitive Research (EPSCoR). This work investigates Joule heating as a solar active region atmosphere heating mechanism in particular in the lower chromosphere where Cowling resistivity is dominant. The team will focus on target structures where strong gradients in the magnetic field strength and field orientation are prevalent resulting in currents such as light bridges (LBs) 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 conduct this investigation, they will make 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. The Joule heating focused on is a function of Cowling resistivity and electric current. To calculate the Cowling resistivity, the team will model the chromosphere as a non-LTE plasma consisting of purely hydrogen which can be described by a quasi-magnetohydrodynamic single-fluid theory in which the interactions between ions and neutrals are followed by the Cowling resistivity. According to this model, Cowling resistivity is a function of plasma bulk density, temperature, magnetic field, electron and ion densities. The team will obtain the magnetic field by applying a non-force-free field (NFFF) extrapolation technique to NASA’s Solar Dynamics Observatory vector magnetograms, the temperature, electron density and/or electron pressure by inverting spectral data from NASA’s Interface Region Imaging Spectrograph and NSF’s Dunn Solar Telescope, and the rest of the quantities from theoretical and semi-empirical atmosphere models. They will make a state-of-the-art data-constrained analysis to calculate the Joule heating for a set of targets in three different observational periods. This investigation will be an important contribution to the existing efforts on chromospheric heating research. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.