WAVE DAMPING OBSERVED IN UPWARDLY PROPAGATING SAUSAGE-MODE OSCILLATIONS CONTAINED WITHIN A MAGNETIC PORE

Abstract

We present observational evidence of compressible magnetohydrodynamic wave modes propagating from the solar photosphere through to the base of the transition region in a solar magnetic pore. High cadence images were obtained simultaneously across four wavelength bands using the Dunn Solar Telescope. Employing Fourier and wavelet techniques, sausage-mode oscillations displaying significant power were detected in both intensity and area fluctuations. The intensity and area fluctuations exhibit a range of periods from 181 412 s, with an average period 290 s, consistent with the global p -mode spectrum. Intensity and area oscillations present in adjacent bandpasses were found to be out-of-phase with one another, displaying phase angles of 6: 12 ◦ , 5: 82 ◦ and 15: 97 ◦ between 4170 u A continuum – G-band, G-band – Na I D1 and Na I D1 – Ca II K heights, respectively, reiterating the presence of upwardly-propagating sausage-mode waves. A phase relationship of 0 ◦ between same-bandpass emission and area perturbations of the pore best categorises the waves as belonging to the ‘slow’ regime of a dispersion diagram. Theoretical calculations reveal that the waves are surface modes, with initial photospheric energies in excess of 35000 Wm 2 . The wave energetics indicate a substantial decrease in energy with atmospheric height, confirming that magnetic pores are able to transport waves that exhibit appreciable energy damping, which may release considerable energy into the local chromospheric plasma. Subject headings: Magnetohydrodynamics (MHD) – Sun: Chromosphere – Sun: Oscillations – Sun: Photosphere