The formation and heating of chromospheric fibrils in a radiation-MHD simulation

TL;DR

This study uses radiation-MHD simulations with passive tracers to analyze the formation and destruction of chromospheric fibrils, revealing that twisted fieldlines and Lorentz forces play key roles in fibril dynamics.

Contribution

It introduces a novel analysis of fibril dynamics using corks and field line tracing, highlighting mechanisms different from shock-driven models.

Findings

Fibril loading involves untwisting of low-lying twisted fieldlines.

Mass drainage occurs predominantly towards footpoints under gravity.

Horizontal velocities can elevate material, causing parabolic motions.

Abstract

Aims: We examine the movements of mass elements within dense fibrils using passive tracer particles (corks) in order to understand fibril creation and destruction processes. Methods: Simulated fibrils were selected at times when they were visible in an H$\alpha$ image proxy. The corks were selected within fibril H$\alpha$ formation regions. From this set, a cork was selected, and the field line passing through it was constructed. Other fibrilar corks close to this fieldline were also selected. Pathlines were constructed, revealing the locations of the mass elements forward and backward in time. The forces acting on these mass elements were analysed. Results: The main process of fibrilar loading in the simulation is different to the mass loading scenario in which waves steepen into shocks and push material upwards along the fieldlines from near their footpoints. Twisted low lying fieldlines were destabilised and then they untwisted, lifting the material trapped above their apexes via the Lorentz force. Subsequently, the majority of the mass drained down the fieldlines towards one or both footpoints under gravity. Material with large horizontal velocities could also elevated in rising fieldlines, creating somewhat parabolic motions, but material was not generally moving upward along a stationary magnetic fieldline during loading. Conclusions: The processes observed in the simulation are plausible additional scenarios. Criteria for observing such events are described. It is desirable that our simulations can also form more densely-packed fibrils from material fed from the base of field footpoints. Experimental parameters required to achieve this are discussed.