Coronal rain in magnetic arcades: Rebound shocks, Limit cycles, and Shear flows

TL;DR

This study uses high-resolution, long-duration magnetohydrodynamic simulations to analyze coronal rain in magnetic arcades, revealing limit cycles, rebound shocks, shear flows, and blob fragmentation mechanisms.

Contribution

It demonstrates for the first time in 2.5D simulations that coronal rain can occur in limit cycles and explores the dynamics of shear flows and blob fragmentation.

Findings

Coronal rain occurs in limit cycles in 2.5D simulations.

Shear flows with velocities around 80 km/s influence blob deformation.

Blob fragmentation occurs within minutes due to shear flows.

Abstract

We extend our earlier multidimensional, magnetohydrodynamic simulations of coronal rain occurring in magnetic arcades with higher resolution, grid-adaptive computations covering a much longer ($>6$ hour) timespan. We quantify how in-situ forming blob-like condensations grow along and across field lines and show that rain showers can occur in limit cycles, here demonstrated for the first time in 2.5D setups. We discuss dynamical, multi-dimensional aspects of the rebound shocks generated by the siphon inflows and quantify the thermodynamics of a prominence-corona-transition-region like structure surrounding the blobs. We point out the correlation between condensation rates and the cross-sectional size of loop systems where catastrophic cooling takes place. We also study the variations of the typical number density, kinetic energy and temperature while blobs descend, impact and sink into the transition region. In addition, we explain the mechanisms leading to concurrent upflows while the blobs descend. As a result, there are plenty of shear flows generated with relative velocity difference around 80 km s$^{-1}$ in our simulations. These shear flows are siphon flows set up by multiple blob dynamics and they in turn affect the deformation of the falling blobs. In particular, we show how shear flows can break apart blobs into smaller fragments, within minutes.