On standing sausage waves in photospheric magnetic waveguides

TL;DR

This paper detects and analyzes standing slow and fast MHD sausage waves in photospheric magnetic waveguides like sunspots and pores, using high-resolution imaging and advanced wavelet analysis, revealing their potential as tools for solar magneto-seismology.

Contribution

It provides the first observational evidence of both fast and slow MHD sausage waves in photospheric waveguides and suggests their role as standing harmonics for probing solar sub-structures.

Findings

Detection of both fast and slow MHD sausage waves in three magnetic waveguides.

Identification of these waves as potential standing harmonics.

Support for using these oscillations in solar magneto-seismology.

Abstract

By focusing on the oscillations of the cross-sectional area and the intensity of magnetic waveguides located in the lower solar atmosphere, we aim to detect and identify magnetohydrodynamic (MHD) sausage waves. Capturing several series of high-resolution images of pores and sunspots and employing 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 representative examples of MHD waveguides in the lower solar atmosphere. The sunspots and pore display a range of periods from 4 to 65 minutes. The sunspots support longer periods than the pore - generally enabling a doubling or quadrupling of the maximum pore oscillatory period. All of these structures display area oscillations indicative of MHD sausage modes and in-phase behaviour between the area and intensity, presenting mounting evidence for the presence of the slow sausage mode within these waveguides. The presence of fast and slow MHD sausage waves has been detected in three different magnetic waveguides in the lower solar photosphere. Furthermore, these oscillations are potentially standing harmonics supported in the waveguides which are sandwiched vertically between the temperature minimum in the lower solar atmosphere and the transition region. Standing harmonic oscillations, by means of solar magneto-seismology, may allow insight into the sub-resolution structure of photospheric MHD waveguides.