Modeling multiphase plasma in the corona: prominences and rain

TL;DR

This review synthesizes how multiphase coronal plasma—comprising hot tenuous and cool dense components—forms in prominences and coronal rain via thermal instability under realistic heating, cooling, and magnetic topologies. It connects 1D evaporation-condensation and 2D/3D MHD evolutions to explain when condensations become stable prominences or rain, and how magnetic dips, flux ropes, and reconnection shape their morphology and lifecycle. The work highlights linear MHD spectroscopy, including thermal continua and convective continua, as a unifying framework for predicting where condensations arise and how they evolve, then demonstrates these concepts across progressively complex dimensional models. It also discusses postflare rain, broader astrophysical contexts, and pressing open problems, such as the need for non-LTE radiative transfer, partial ionization effects, and data-driven, high-resolution simulations to fully capture fine-structure and dynamics. Overall, the findings advance our understanding of how coronal heating and radiative losses orchestrate the formation and evolution of multiphase solar structures with significant implications for solar activity and space weather.

Abstract

We review major achievements in our understanding of multiphase coronal plasma, where cool-dense and hot-tenuous matter coexists, brought about by advances in modeling and theory, inspired by observations. We give an overview of models that self-consistently form solar (or stellar) prominences and filaments, or (postflare) coronal rain, and clarify how these different phenomena share a common physical origin, relating radiative losses and coronal heating. While we do not fully understand the coronal heating, multi-dimensional models of solar prominence and rain formation demonstrate how thermal instability triggers condensations, and how their morphology may reveal aspects of the applied heating at play. We emphasize how the many pathways to linear instability due to combined ingredients of heat-loss, gravity, flows, and magnetic topologies are all involved in the resulting nonlinear magnetohydrodynamics. We provide some challenges to future model efforts, especially concerning prominence fine structure, internal dynamics, and their overall lifecycle.

Figures (20)

• Figure 1: H$\alpha$ images made by the CHASE mission CHASE2022, where we see a typical prominence (at left, in emission above the limb) versus a clear filament view (at right). Figure credit: Yiwei Ni (Nanjing University).
• Figure 2: A force-balanced flux rope with helical magnetic field lines (red) where higher density matter rests as stacked in the dips (gray isosurfaces). The cross-sectional variation (in blue) quantifies pressure throughout the flux rope, from Blokland2011B.
• Figure 3: The magnetofrictional evolution of a large spherical dipole region (panel (a)), when subjected to synthetic supergranular motions that impact the magnetogram (panels (b) through (f)). Eventually, a large-scale nonlinear force-free field that has a magnetic flux rope topology emerges (panel (f)). From CHUN2024.
• Figure 4: The 3D density structure resulting from TI in a local coronal volume. The view at right also shows (in red) the background (nearly) homogeneous magnetic field, clearly not aligning with the condensation fine structure. From Claes2020.
• Figure 5: For a realistic solar atmosphere (with temperature-density as function of height) from photosphere to corona, augmented with a horizontal, uniform 10 G field, a full spectroscopic analysis identifies all shaded regions as containing unstable thermal (top left panel a) or overstable slow (top right panel b) eigenmodes. All panels have height varying horizontally, and the top panels also vary the angle $\theta$ between the horizontal wavevector and the magnetic field. At the specific angle indicated by a dashed horizontal line in panels a and b, the lower panels show the growthrates of thermal (bottom left panel c) or slow (bottom right panel d) modes. From Claes2021.