Unveiling the True Nature of Plasma Dynamics from the Reference Frame of a Super-penumbral Fibril

TL;DR

This study re-projects wave oscillations in solar fibrils to better understand their propagation and damping, revealing a propagating kink wave with specific properties and highlighting challenges in modeling wave damping mechanisms.

Contribution

It introduces a novel re-projection method to analyze transverse wave oscillations in fibrils, improving the understanding of wave dynamics in the solar atmosphere.

Findings

Identified a propagating kink oscillation with a 430 s period and 69 km/s phase velocity.

Observed wave damping with a length of approximately 9.2 Mm and energy flux decrease.

Found that existing damping models cannot fully explain the observed damping length.

Abstract

The magnetic geometry of the solar atmosphere, combined with projection effects, makes it difficult to accurately map the propagation of ubiquitous waves in fibrillar structures. These waves are of interest due to their ability to carry energy into the chromosphere and deposit it through damping and dissipation mechanisms. To this end, the Interferometric Bidimensional Spectrometer (IBIS) at the Dunn Solar Telescope was employed to capture high resolution H$\alpha$ spectral scans of a sunspot, with the transverse oscillations of a prominent super-penumbral fibril examined in depth. The oscillations are re-projected from the helioprojective-cartesian frame to a new frame of reference oriented along the average fibril axis through non-linear force-free field extrapolations. The fibril was found to be carrying an elliptically polarised, propagating kink oscillation with a period of $430$ s and a phase velocity of $69\pm4$ km s$^{-1}$. The oscillation is damped as it propagates away from the sunspot with a damping length of approximately $9.2$ Mm, resulting in the energy flux decreasing at a rate on the order of $460$ W m$^{-2}$/Mm. The H$\alpha$ line width is examined and found to increase with distance from the sunspot; a potential sign of a temperature increase. Different linear and non-linear mechanisms are investigated for the damping of the wave energy flux, but a first-order approximation of their combined effects is insufficient to recreate the observed damping length by a factor of at least $3$. It is anticipated that the re-projection methodology demonstrated in this study will aid with future studies of transverse waves within fibrillar structures.