Transverse waves observed in a fibril with the MiHI prototype

¹ Centre for mathematical Plasma Astrophysics, Mathematics Department, KU Leuven, Celestijnenlaan 200B bus 2400, B-3001 Leuven, Belgium
² Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
³ Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Ringlaan -3- Av. Circulaire, 1180 Brussels, Belgium

^⋆ Corresponding author: elena.petrova@kuleuven.be

Received: 8 November 2024
Accepted: 20 March 2025

Abstract

Context. Fine-scale structures of the solar chromosphere, particularly fibrils, are known to host various types of magnetohydrodynamic (MHD) waves that can transport energy to the corona. In particular, absorption features observed in the Hα channel have been widely detected that exhibit transverse oscillations.

Aims. We aimed to detect a high-frequency transverse oscillation in fibrils.

Methods. We conducted a case study on a high-frequency transverse oscillation in a chromospheric fibril. A chromospheric fibril was observed on 24 August 2018, in the Hα spectral line, with the prototype Microlensed Hyperspectral Imager (MiHI) at the Swedish 1-meter Solar Telescope. The MiHI instrument is an integral field spectrograph capable of achieving ultra-high resolution simultaneously in the spatial, temporal, and spectral domains.

Results. The detected oscillation characteristics include a period of 15 s and a displacement amplitude of 42 km. Using the bisector method, we derived Doppler velocities and determined that the polarisation of the oscillation was elliptical.

Conclusions. The energy contained in the oscillation ranges from 390 to 2300 W/m², which is not sufficient to balance radiative losses of the chromosphere.