First evidence of interaction between longitudinal and transverse waves in solar magnetic elements

TL;DR

This study provides the first observational evidence of interaction between longitudinal and transverse waves in small solar magnetic elements, supporting theories of MHD wave excitation by granular flows.

Contribution

It demonstrates the coexistence and interaction of transverse and longitudinal oscillations in small magnetic elements, confirmed by high-resolution observations and MHD simulations.

Findings

Transverse oscillations with amplitudes of 1-2 km/s are common.

Longitudinal oscillations with amplitudes around 0.4 km/s are observed.

Transverse and longitudinal waves show a +-90 degrees phase lag at maximum coherence.

Abstract

Small-scale magnetic fields are thought to play an important role in the heating of the outer solar atmosphere. By taking advantage of the unprecedented high-spatial and temporal cadence of IMaX, the filter vector polarimeter on board the Sunrise balloon-borne observatory, we study the transversal and longitudinal velocity oscillations in small magnetic elements. The results of this analysis are then compared to MHD simulations, showing excellent agreement. We found buffeting-induced transverse oscillations with velocity amplitudes of the order of 1-2 km/s, to be common along with longitudinal oscillations with amplitudes 0.4 km/s. Moreover, we also found an interaction between transverse oscillations and longitudinal velocity oscillations, showing a +-90 degrees phase lag at the frequency at which they exhibit the maximum coherence in the power spectrum. Our results are consistent with the theoretical picture in which MHD longitudinal waves are excited inside small magnetic elements as a response of the flux tube to the forcing action of the granular flows.