Observational evidence for buffeting induced kink waves in solar magnetic elements

TL;DR

This study provides observational evidence that turbulent convection in the solar photosphere excites kink waves in magnetic elements, which may contribute to the energy transfer in the Sun's upper atmosphere.

Contribution

It introduces the use of empirical mode decomposition to analyze non-stationary transverse oscillations in magnetic flux tubes, revealing sub-harmonic kink modes induced by convective buffeting.

Findings

Detection of low frequency kink oscillations with a 7.6-minute period.

Identification of sub-harmonics of fundamental kink modes.

Evidence linking convection buffeting to wave excitation.

Abstract

The role of diffuse photospheric magnetic elements in the energy budget of the upper layers of the Sun's atmosphere has been the recent subject of many studies. This was made possible by the availability of high temporal and spatial resolution observations of the solar photosphere, allowing large numbers of magnetic elements to be tracked to study their dynamics. In this work we exploit a long temporal series of seeing-free magnetograms of the solar photosphere to study the effect of the turbulent convection in the excitation of kink oscillations in magnetic elements. We make use of the empirical mode decomposition technique (EMD) in order to study the transverse oscillations of several magnetic flux tubes. This technique permits the analysis of non-stationary time series like those associated to the horizontal velocities of these flux tubes which are continuously advected and dispersed by granular flows. Our primary findings reveal the excitation of low frequency modes of kink oscillations, which are sub-harmonics of a fundamental mode with a $7.6 \pm 0.2$ minute periodicity. These results constitute a strong case for observational proof of the excitation of kink waves by the buffeting of the convection cells in the solar photosphere, and are discussed in light of their possible role in the energy budget of the upper Sun's atmosphere.