The Sun at millimeter wavelengths

V. Magnetohydrodynamic waves in a fibrillar structure

¹ Rosseland Centre for Solar Physics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
² Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
³ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁴ Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen, Denmark
⁵ Geophysical and Astronomical Observatory, Faculty of Science and Technology, University of Coimbra, Coimbra, Portugal
⁶ Instituto de Astrofísica e Ciências do Espaço, Department of Physics, University of Coimbra, Coimbra, Portugal
⁷ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
⁸ Department of Physics and Astronomy, California State University Northridge, Northridge, CA 91330, USA
⁹ ASI Italian Space Agency, Via del Politecnico snc, I-00133 Rome, Italy

^⋆ Corresponding author; maryam.saberi@astro.uio.no

Received: 8 August 2024
Accepted: 23 November 2024

Abstract

Magnetohydrodynamic (MHD) waves, playing a crucial role in transporting energy through the solar atmosphere, manifest in various chromospheric structures. Here, we investigated MHD waves in a long-lasting dark fibril using high-temporal-resolution (2 s cadence) Atacama Large Millimeter/submillimeter Array (ALMA) observations in Band 6 (centered at 1.25 mm). We detected oscillations in brightness temperature, horizontal displacement, and width at multiple locations along the fibril, with median periods and standard deviations of 240 ± 114 s, 225 ± 102 s, and 272 ± 118 s, respectively. Wavelet analysis revealed a combination of standing and propagating waves, suggesting the presence of both MHD kink and sausage modes. Less dominant than standing waves, oppositely propagating waves exhibit phase speeds (median and standard deviation of distributions) of 74 ± 204 km/s, 52 ± 197 km/s, and 28 ± 254 km/s for the three observables, respectively. This work demonstrates ALMA’s capability to effectively sample dynamic fibrillar structures, despite previous doubts. This provides valuable insights into wave dynamics in the upper chromosphere.