Formation and heating of chromospheric fibrils in a radiation-MHD simulation^⋆

¹ Institute for Solar Physics, Department of Astronomy, Stockholm University, AlbaNova University Centre, 106 91 Stockholm, Sweden
e-mail: malcolm.druett@astro.su.se
² Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
³ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
⁴ Rosseland Centre for Solar Physics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway

Received: 8 October 2021
Accepted: 22 June 2022

Abstract

Aims. We examine the movements of mass elements within dense fibrils using passive tracer particles (corks) in order to understand the creation and destruction processes of fibrils.

Methods. Simulated fibrils were selected at times when they were visible in a Hα image proxy. The corks were selected within fibril Hα formation regions. From this set, we selected a cork and constructed the field line passing through it. Other fibrilar corks close to this field line were also selected and pathlines were constructed, revealing the locations of the mass elements forwards and backwards in time. Finally, we analysed the forces acting on these mass elements.

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 field lines from locations near their footpoints. The twisted, low-lying field lines 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 field lines towards one or both footpoints under the influence of gravity. Material with large horizontal velocities could also be elevated in rising field lines, creating somewhat parabolic motions, but the material was not generally moving upward along a stationary magnetic field line during loading.

Conclusions. The processes observed in the simulation are additional scenarios that are plausible. The criteria for observing such events are described in this work. We note that it is desirable for our simulations to also be able to form more densely packed fibrils from material fed from the base of field footpoints. The experimental parameters required to achieve this are also discussed in this paper.