High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI

TL;DR

This study analyzes high-frequency waves in small solar magnetic elements using high-resolution observations, revealing upward propagating waves, different wave types, and estimating wave travel times and phase speeds in the lower solar atmosphere.

Contribution

It provides the first detailed characterization of wave propagation in small magnetic elements at high spatial and temporal resolution, including phase speed estimates and wave type distinctions.

Findings

Upward propagating waves observed up to 30 mHz.

Both compressible and kink waves detected in magnetic features.

Estimated height difference of ~450 km between atmospheric layers.

Abstract

We characterize waves in small magnetic elements and investigate their propagation in the lower solar atmosphere from observations at high spatial and temporal resolution. We use the wavelet transform to analyze oscillations of both horizontal displacement and intensity in magnetic bright points found in the 300 nm and the Ca II H 396.8 nm passbands of the filter imager on board the Sunrise balloon-borne solar observatory. Phase differences between the oscillations at the two atmospheric layers corresponding to the two passbands reveal upward propagating waves at high frequencies (up to 30 mHz). Weak signatures of standing as well as downward propagating waves are also obtained. Both compressible and incompressible (kink) waves are found in the small-scale magnetic features. The two types of waves have different, though overlapping, period distributions. Two independent estimates give a height difference of approximately 450+-100 km between the two atmospheric layers sampled by the employed spectral bands. This value, together with the determined short travel times of the transverse and longitudinal waves provide us with phase speeds of 29+-2 km/s and 31+-2 km/s, respectively. We speculate that these phase speeds may not reflect the true propagation speeds of the waves. Thus, effects such as the refraction of fast longitudinal waves may contribute to an overestimate of the phase speed.