A research team from the Yunnan Observatories of the Chinese Academy of Sciences (CAS) has conducted a systematic study of transverse oscillations and associated energy transport in solar chromospheric fibrils, using high-resolution observations from the four-meter Daniel K. Inouye Solar Telescope (DKIST). The findings were published in The Astrophysical Journal on Oct. 15.

Fibrils are ubiquitous chromospheric structures aligned with magnetic field lines, acting as waveguides for magnetohydrodynamic (MHD) wave propagation and energy transport. Studying their transverse oscillations is key to understanding chromospheric and coronal heating. However, limited spatial and temporal resolution has left high-frequency, small-amplitude oscillations unresolved, leaving their statistical properties and energy-transport contributions poorly characterized.

The team analyzed high-resolution Hα observations of a quiet-Sun region and an active region, obtained by the Visible Broadband Imager (VBI) aboard DKIST on Aug. 29, 2023, and Aug. 27, 2024, respectively. Using the Automatic Northumbria University Wave Tracking algorithm (Auto-NUWT), the researchers systematically analyzed the transverse oscillations of the fibrils.

A total of 22,866 oscillation measurements were obtained, revealing that high-frequency, small-amplitude transverse oscillations were highly prevalent in fibrils across different magnetic environments. The detected oscillations exhibited a mean period of approximately 56 ± 49 seconds, a displacement amplitude of 37 ± 25 km, and a velocity amplitude of 6 ± 4 km s^-1.

Furthermore, by comparing oscillation signals at adjacent positions along the fibrils, the researchers obtained 3,244 reliable measurements of propagating waves, with a characteristic phase speed of approximately 21 ± 13 km s^-1. These oscillation characteristics were consistent with Alfvénic kink-mode waves. Based on the wave parameters, the estimated energy flux carried by the detected transverse kink waves was approximately 20 to 200 W m^-2.

The study reveals a widespread population of high-frequency, small-amplitude transverse waves in solar chromospheric fibrils that previous statistical investigations had insufficiently characterized. Compared with the oscillation periods reported in earlier observations, the substantially shorter periods identified in this study suggest that previous observations may have missed a significant population of small-amplitude, high-frequency waves.

Although the estimated wave energy flux alone is insufficient to sustain chromospheric heating, these findings provide new observational constraints on MHD wave propagation and energy transport in the solar chromosphere. Moreover, the results highlight the unprecedented capabilities of DKIST in resolving fine-scale structures and rapid dynamical processes in the solar atmosphere.

This work was supported by the CAS Strategic Priority Research Program, the National Key R&D Program of China, and other grants.