Inferring the Coronal Density Irregularity From Euv Spectra

Abstract

Understanding the density structure of the solar corona is important for modeling both coronal heating and the solar wind. Direct measurements are difficult because of line-of-sight integration and possible unresolved structures. We present a new method for quantifying such structures using density-sensitive extreme ultraviolet line intensities to derive a density irregularity parameter, a relative measure of the amount of structure along the line of sight. We also present a simple model to relate the inferred irregularities to physical quantities, such as the filling factor and density contrast. For quiet-Sun regions and interplume regions of coronal holes, we find a density contrast of at least a factor of 3-10and corresponding filling factors of about 10%-20%. Our results are in rough agreement with other estimates of the density structures in these regions. The irregularity diagnostic provides a useful relative measure of unresolved structure in various regions of the corona.

How transverse MHD wave-driven turbulence influences the density filling factor in the solar corona?

“…E.g. Hahn & Savin (2016) have estimated the filling factor for quiet-Sun and interplume regions of coronal holes using "two-density slab model", where they have estimated the filling factors are ≈ 10% − 20%. From the spectroscopic observation, the filling factor is found to be 0.10 for an active region loop (Warren et al 2008), and 0.30 for a cooling loop in quiescent active regions (Landi et al 2009).…”

“…The study of the filling factors helps us to understand the overall density structure, and how the overdense regions are spatially distributed in the medium. This gives an estimation of the density inhomogeneity of the medium (Hahn & Savin 2016). On the other hand, kink waves (body waves) have maximum wave energy inside the overdense plasma structures, while the surface waves (Alfvén waves) have energy concentrated at the boundaries of it (Van Doorsselaere et al 2014).…”

“…Filling factor in the open magnetic structures (e.g. coronal holes (CHs), coronal bright points, plumes, interplumes, moss regions) has been calculated in past (Warren et al 2008;Tripathi et al 2010;Hahn & Savin 2016). These regions are the open magnetic structures, where the magnetic field lines rise but never come back in the same horizontal plane within the region of interest (Sen & Mangalam 2019).…”

“…Verbeeck et al (2014) have calculated the filling factors varying from 0.02 to 0.22 in active regions and 0.02 to 0.18 in the quiet sun regions. Hahn & Savin (2016) have inferred the filling factors using "Two-slab density model" in the coronal holes, plume, interplume, and quiet sun regions observed by EIS/Hinode data. They have found the filling factors to vary between 0.10 to 0.20 in the interplume regions, 0.004 to 0.02 in the plumes, and 0.10 in the CHs and QS regions.…”