High-frequency oscillations in small chromospheric bright features observed with Atacama Large Millimetre/Submillimetre Array

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. 2s cadence) with the Atacama large millimetre/ submillimetre array (ALMA) in Band 3 (centred at 3mm; 100GHz), exhibit three small-scale features with oscillatory behaviour with different, but overlapping, distributions of period on the order of, on average, 9022s, 110 +/- 12s and 66 +/- 23s, 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 also suggest the presence of Alfvenic 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. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.

Automated summary

Detection of oscillations in brightness temperature, size and horizontal velocity of small bright features in the chromosphere suggests the presence of fast sausage-mode waves and possibly Alfvenic oscillations. These high-frequency magnetohydrodynamic waves may channel energy into the outer atmosphere of the Sun.