Spectroscopic Analysis and Image Processing of the Optically-Thin Solar Corona

Abstract

This thesis examines the emission, radiative transfer, and interpretation of spectral observations of the optically-thin solar corona. The first half of this work presents a forward model called the Global Heliospheric Optically-thin Spectral Transport Simulation (GHOSTS), which uses data from other physical models to determine the plasma parameters in the solar environment. The model then performs optically-thin radiative transfer through the corona for a set of commonly observed coronal ions, generating ensembles of simulated lines. We develop GHOSTS starting with a time-steady model, and we focus on characterizing spectral lines that are influenced by three primary factors: solar wind outflow, preferential ion heating, and non-equilibrium ion populations along the Line-of-Sight (LOS) due to strong temperature gradients. We extend the GHOSTS model into the time domain to characterize how the spectral lines are affected by dynamic phenomena like dense magnetic polar plumes along the LOS shaken by Alfvén waves propagating outward from the photosphere. The photosphere is very bright relative to the corona, so these two regions cannot be readily examined at the same time, even when they are both observed together. In the second half of this work, we review the literature regarding algorithms that are commonly applied to High Dynamic Range (HDR) filtergram imagery of the corona, like those recorded by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO). We then present two new tools for examining these images, and evaluate them relative to algorithms from the literature: Quantile Radial Normalization (QRN) is a variation of a traditional Radial Graded Filter (RGF) that normalizes the image using percentile curves. The Radial Histogram Equalizing Filter (RHEF) is a more powerful algorithm, a hybrid of RGF and Adaptive Histogram Equalization (AHE), which equalizes the histogram of intensity at each radius. We conclude by offering a brief overview of the preliminary work we have performed modeling polarization observations for the PUNCH mission.