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

¹ Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
e-mail: stangalini@mps.mpg.de
² School of Space Research, Kyung Hee University, Yongin, 446-701 Gyeonggi, Republic of Korea
³ IAC Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain

Received: 17 December 2012
Accepted: 24 April 2013

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 the Imaging Magnetograph eXperiment (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 magnetohydrodynamic (MHD) simulations, showing excellent agreement. We found buffeting-induced transverse oscillations with velocity amplitudes of the order of 1–2 km s^-1 to be common along with longitudinal oscillations with amplitudes ~0.4 km s^-1. Moreover, we also found an interaction between transverse oscillations and longitudinal velocity oscillations, showing a ± 90° 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.