Standing sausage waves in photospheric magnetic waveguides

¹ Slovak Central Observatory, PO Box 42, 94701 Hurbanovo, Slovak Republic
e-mail: ivan.dorotovic@suh.sk
² Solar Physics & Space Plasma Research Centre (SP 2RC), School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK
e-mail: robertus@sheffield.ac.uk; n.freij@sheffield.ac.uk
³ Hlohovec Observatory and Planetarium, Sládkovičova 41, 92001 Hlohovec, Slovak Republic
e-mail: astrokar@hl.cora.sk
⁴ Instituto de Astrofísica de Canarias, 38205, La Laguna, Tenerife, Spain
e-mail: imarquez@ull.es

Received: 11 October 2012
Accepted: 4 December 2013

Abstract

Aims. By focussing on the oscillations of the cross-sectional area and the total intensity of magnetic waveguides located in the lower solar atmosphere, we aim to detect and identify magnetohydrodynamic (MHD) sausage waves.

Methods. Capturing several high-resolution time series of magnetic waveguides and employing a wavelet analysis, in conjunction with empirical mode decomposition (EMD), makes the MHD wave analysis possible. For this paper, two sunspots and one pore (with a light bridge) were chosen as examples of MHD waveguides in the lower solar atmosphere.

Results. The waveguides display a range of periods from 4 to 65 min. These structures display in-phase behaviour between the area and intensity, presenting mounting evidence for sausage modes within these waveguides. The detected periods point towards standing oscillations.

Conclusions. The presence of fast and slow MHD sausage waves has been detected in three different magnetic waveguides in the solar photosphere. Furthermore, these oscillations are potentially standing harmonics supported in the waveguides that are sandwiched vertically between the temperature minimum in the lower solar atmosphere and the transition region. The relevance of standing harmonic oscillations is that their exploitation by means of solar magneto-seismology may allow insight into the sub-pixel resolution structure of photospheric MHD waveguides.