The Cooling of Coronal Plasmas. iv: Catastrophic Cooling of Loops

TL;DR

This paper investigates the process of catastrophic cooling in coronal loops, revealing that a critical temperature threshold causes rapid temperature drops with minimal density change, significantly affecting plasma lifetime.

Contribution

It introduces an analytic framework for understanding catastrophic cooling in coronal loops and identifies the critical temperature thresholds across different solar conditions.

Findings

Catastrophic cooling occurs below a critical temperature.

Analytic expressions match numerical simulations.

Cooling limits plasma lifetime below critical temperature.

Abstract

We examine the radiative cooling of coronal loops and demonstrate that the recently identified catastrophic cooling (Reale and Landi, 2012) is due to the inability of a loop to sustain radiative / enthalpy cooling below a critical temperature, which can be > 1 MK in flares, 0.5 - 1 MK in active regions and 0.1 MK in long tenuous loops. Catastrophic cooling is characterised by a rapid fall in coronal temperature while the coronal density changes by a small amount. Analytic expressions for the critical temperature are derived and show good agreement with numerical results. This effect limits very considerably the lifetime of coronal plasmas below the critical temperature.