Transverse Oscillations in Slender Ca II H Fibrils Observed with Sunrise/SuFI

TL;DR

This study reports high-resolution observations of transverse, likely Alfvenic, kink waves in slender Ca II H fibrils in the lower solar chromosphere, revealing their properties, propagation, and potential energy contribution to chromospheric heating.

Contribution

First detailed measurement of transverse oscillations in Ca II H fibrils in the lower chromosphere using Sunrise/SuFI data, highlighting their wave characteristics and energy flux.

Findings

Transverse waves have median amplitudes of 2.4 km/s and periods of 83 s.

Waves propagate with median phase speeds of 9 km/s, sometimes in both directions.

Estimated energy flux of these waves is about 15 kW/m^2.

Abstract

We present observations of transverse oscillations in slender Ca II H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long time series of high- (spatial and temporal-) resolution seeing-free observations in a 0.11 nm wide passband covering the line core of Ca II H 396.9 nm from the second flight of the Sunrise balloon-borne solar observatory. The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures. Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes and periods on the order of 2.4+-0.8 km/s and 83+-29 s, respectively (with standard deviations given as uncertainties). We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9+-14 km/s. While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed. The transverse oscillations are likely Alfvenic and are thought to be representative of magnetohydrodynamic kink waves. The wave propagation suggests that the rapid high-frequency transverse waves, often produced in the lower photosphere, can penetrate into the chromosphere with an estimated energy flux of ~ 15 kW/m^2. Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere.