Dynamics of solar coronal loops II. Catastrophic cooling and high-speed downflows

TL;DR

This paper models plasma condensation and catastrophic cooling in solar coronal loops, revealing dynamic behaviors like high-speed downflows and transient brightenings, aligning with observations and explaining recent bright blob phenomena.

Contribution

It introduces a new numerical model showing how footpoint-concentrated heating leads to catastrophic cooling and dynamic plasma features in coronal loops.

Findings

Recurrent plasma condensations with high-speed downflows observed.

Transient brightenings of transition region lines match TRACE data.

Explains moving bright blobs in large coronal loops.

Abstract

This work addresses the problem of plasma condensation and ``catastrophic cooling'' in solar coronal loops. We have carried out numerical calculations of coronal loops and find several classes of time-dependent solutions (static, periodic, irregular), depending on the spatial distribution of a temporally constant energy deposition in the loop. Dynamic loops exhibit recurrent plasma condensations, accompanied by high-speed downflows and transient brightenings of transition region lines, in good agreement with features observed with TRACE. Furthermore, these results also offer an explanation for the recent EIT observations of De Groof et al. (2004) of moving bright blobs in large coronal loops. In contrast to earlier models, we suggest that the process of catastrophic cooling is not initiated by a drastic decrease of the total loop heating but rather results from a loss of equilibrium at the loop apex as a natural consequence of heating concentrated at the footpoints of the loop, but constant in time.