High-frequency oscillations in small chromospheric bright features observed with ALMA

TL;DR

This study uses high-resolution ALMA observations to detect high-frequency magnetohydrodynamic waves in small chromospheric features, revealing potential energy transfer mechanisms in the solar atmosphere.

Contribution

First detection of high-frequency oscillations in small chromospheric features using ALMA, highlighting the diagnostic potential for solar atmospheric wave studies.

Findings

Detection of oscillations with periods around 66-110 seconds.

Anti-correlation between brightness temperature and size indicating sausage-mode waves.

Possible identification of Alfvénic kink oscillations.

Abstract

We report detection of oscillations in brightness temperature, size, and horizontal velocity of three small bright features in the chromosphere of a plage/enhanced-network region. The observations, which were taken with high temporal resolution (i.e., 2-sec cadence) with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with oscillatory behaviour with different, but overlapping, distributions of period on the order of, on average, $90 \pm 22$ s, $110 \pm 12$ s and $66 \pm 23$ s, respectively. We find anti-correlations between perturbations in brightness temperature and size of the three features, which suggest the presence of fast sausage-mode waves in these small structures. In addition, the detection of transverse oscillations (although with a larger uncertainty) may suggest as well the presence of Alfv\'enic oscillations which are likely representative of kink waves. This work demonstrates the diagnostic potential of high-cadence observations with ALMA for detecting high-frequency magnetohydrodynamic waves in the solar chromosphere. Such waves can potentially channel a vast amount of energy into the outer atmosphere of the Sun.