Multithermal apparent damping of slow waves due to strands with a Gaussian temperature distribution

¹ Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
e-mail: tom.vandoorsselaere@kuleuven.be
² Aryabhatta Research Institute of Observational Sciences, Nainital, India
³ Indian Institute of Astrophysics, Koramangala, 560034 Bengaluru, India
⁴ Center of Excellence in Space Sciences, IISER, 741246 Kolkata, India
⁵ School of Mathematics and Statistics, University of St Andrews, St Andrews, Fife KY16 9SS, UK

Received: 27 July 2023
Accepted: 23 December 2023

Abstract

Context. Slow waves in solar coronal loops are strongly damped, but the current theory of damping by thermal conduction cannot explain some observational features.

Aims. We investigated the propagation of slow waves in a coronal loop built up from strands of different temperatures.

Methods. We considered the loop to have a multithermal, Gaussian temperature distribution. The different propagation speeds in different strands led to a multithermal apparent damping of the wave, similar to observational phase mixing. We used an analytical model to predict the damping length and propagation speed for the slow waves, including in imaging with filter telescopes.

Results. We compared the damping length due to this multithermal apparent damping with damping due to thermal conduction and found that the multithermal apparent damping is more important for shorter period slow waves. We quantified the influence of instrument filters on the wave’s propagation speed and damping. This allowed us to compare our analytical theory to forward models of numerical simulations.

Conclusions. We find that our analytical model matches the numerical simulations very well. Moreover, we offer an outlook for using the slow wave properties to infer the loop’s thermal properties.