The Distinction Between Thermal Nonequilibrium and Thermal Instability

TL;DR

This paper clarifies the fundamental differences between thermal nonequilibrium and thermal instability in coronal loops, emphasizing their distinct mechanisms and discussing their potential interconnections and implications for solar physics.

Contribution

It provides a clear explanation distinguishing thermal nonequilibrium from thermal instability and explores their possible links in coronal loop dynamics.

Findings

Thermal nonequilibrium involves accelerated cooling and cold condensations.

Thermal instability is a different process with distinct characteristics.

Large-amplitude perturbations may connect the two phenomena.

Abstract

For some forms of steady heating, coronal loops are in a state of thermal nonequilibrium and evolve in a manner that includes accelerated cooling, often resulting in the formation of a cold condensation. This is frequently confused with thermal instability, but the two are in fact fundamentally different. We explain the distinction and discuss situations where they may be interconnected. Large-amplitude perturbations, perhaps associated with MHD waves, likely play a role in explaining phenomena that have been attributed to thermal nonequilibrium but also seem to require cross-field communication.