Physics of Solar Prominences: I—Spectral Diagnostics and Non-LTE Modelling

Abstract

This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE (i.e., when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one-and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences.

The magnetic field in the solar atmosphere

“…On larger (active-region) scales, often observed as dark elongated features in Hα 6563 Å and He i 10830 Å images are filaments ("prominences" when observed above the limb; for reviews see Labrosse et al 2010;Mackay et al 2010). Filaments straddle polarity inversion lines and typically exhibit heights of ≈50 Mm, lengths of ≈200 Mm and a thickness of a few Mm (Stix 2002).…”

The magnetic field configuration of a solar prominence inferred from spectropolarimetric observations in the He i 10 830 Å triplet

“…Prominences, also referred to as filaments when observed against the solar disk, are cool, dense, magnetized formations of 10 4 K plasma embedded in the 10 6 K solar corona (for reviews see Mackay et al 2010;Labrosse et al 2010). They are located above polarity inversion lines (PILs or filament channels), i.e., the line that divides regions of opposite magnetic flux in the photosphere.…”

Proper horizontal photospheric flows in a filament channel

“…Prominences, which are filaments when observed on the disk, are large structures in the solar corona filled with cool dense plasma suspended above magnetic polarity inversion lines (reviews of Mackay et al 2010;Labrosse et al 2010). The formation, the dynamics, and the eruption of solar filaments and prominences are important parts of our understanding of coronal physics and more specifically, the behavior of magnetic fields as they are transported across the solar surface through corona towards the heliosphere via the coronal mass ejections (CME).…”