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 4170Å continuum -G-band, G-band -Na I D 1 and Na I D 1 -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 35 000 W m −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.

The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral Atmosphere

“…propagating slow magnetoacoustic sausage modes in a magnetic pore also reveal a gradual decrease in energy flux with height (Grant et al 2015). As can be seen, a slightly steeper reduction in mechanical wave energy is observed above the Ca II K atmospheric height.…”

On the Properties of Slow MHD Sausage Waves Within Small-Scale Photospheric Magnetic Structures

“…This was previously suggested by Grant et al (2015). Exploiting this relation will allow a comparison to be made between the observed changes in pore area and the magnetic oscillations found from Stokes profiles (e.g., Balthasar et al 2000).…”

“…For another magnetic pore, the percentage change was found to be similar at 6% (Grant et al 2015). Let us now assume that the equilibrium magnetic field strength of the pore takes typical values of 1000-2000 G. Then, the amplitude of the magnetic field oscillations should be 40-140 G. The lower end of this estimated range of percentage change in the magnetic field agrees well with the percentage changes in the magnetic field obtained using Stokes profiles by, for example, Balthasar et al (2000) and Fujimura & Tsuneta (2009).…”

“…Furthermore, these magnetic structures were able to support several oscillations, with periods that were not too dissimilar to standing mode harmonics in an ideal case. Grant et al (2015) observed a magnetic pore within Active Region NOAA 11683, using highresolution scans of multiple heights of the solar atmosphere using ROSA and the Interferometric Bidimensional Spectrometer (IBIS) on the DST. They showed that sausage modes were present in all the observed layers that were damped while they propagated into the higher levels of solar atmosphere.…”

Spatial damping of propagating sausage waves in coronal cylinders

“…While kink waves (with azimuthal wavenumber m = 1) have attracted much attention since their measurements with the Transition Region And Coronal Explorer (TRACE; Nakariakov et al 1999;Aschwanden et al 1999), sausage waves prove important in interpreting secondscale, quasi-periodic pulsations (QPPs) in the light curves of solar flares (see Nakariakov & Melnikov 2009, for a recent review). Their importance is strengthened given their recent detection in both the chromosphere (Morton et al 2012) and photosphere (Dorotovič et al 2014;Grant et al 2015).…”