Statistical Approach on Differential EmissionMeasure of Coronal Holes using the CATCH Catalog

Abstract

Coronal holes are large-scale structures in the solar atmosphere that feature a reduced temperature and density in comparison to the surrounding quiet Sun and are usually associated with open magnetic fields. We perform a differential emission measure analysis on the 707 non-polar coronal holes collected in the Collection of Analysis Tools for Coronal Holes (CATCH) catalog to derive and statistically analyze their plasma properties (i.e. temperature, electron density, and emission measure). We use intensity filtergrams of the six coronal EUV filters from the \textit{Atmospheric Imaging Assembly} onboard of the \textit{Solar Dynamics Observatory}, which cover a temperature range from $\approx 10^{5.5}$ to $10^{7.5}$\,K. Correcting the data for stray and scattered light, we find that all coronal holes have very similar plasma properties with an average temperature of $0.94\pm 0.18$ MK, a mean electron density of $(2.4\pm 0.7)\times 10^8$\,cm${}^{-3}$, and a mean emission measure of $(2.8\pm 1.6)\times 10^{26}$\,cm${}^{-5}$. The temperature distribution within the coronal hole was found to be largely uniform, whereas the electron density shows a $40\%$ linear decrease from the boundary towards the inside of the coronal hole. At distances greater than \SI{20}{\arcsecond} ($\approx 15$\,Mm) from the nearest coronal hole boundary, the density also becomes statistically uniform. The coronal hole temperature may show a weak solar cycle dependency, but no statistically significant correlation of plasma properties to solar cycle variations could be determined throughout the observed time period between 2010 and 2019.

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