2026-10-06T04:18:43Z https://api.figshare.com/v2/oai

oai:figshare.com:article/32639079 2026-10-01T16:42:46Z portal_1172 item_type_8 month_year_10_2026

High resolution wave signatures in the magnetic solar atmosphere Samuel Grant (12442396) PUREID: 552680716 This thesis is concerned with the study of high frequency compressible MHD waves and their potential as energy conduits for the heating of the upper solar atmosphere. High cadence, multi-wavelength ROSA observations were used to investigate the propagation of sausage mode waves in magnetic pores. Employing Fourier and wavelet techniques, sausage-mode oscillations displaying significant power were detected in both intensity and area fluctuations, at range of periods from 181 − 412 s, with an average period ~290 s. Intensity and area oscillations present in adjacent bandpasses were found to be out-of-phase with one another, displaying phase angles consistent with the presence of upwardly-propagating sausage-mode waves. A phase relationship of ~0 degrees 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.<br><br>The surface and body wave modes of sausage mode MHD waves are directly observed for the first time using G-band imaging from ROSA of multiple magnetic pores. The 2-D form of the wave power for these pores was visualised after verification that sausage modes were present. The structuring of the wave power within the geometry of the pore revealed the nature of the wave mode, with the surface mode proving to be more prevalent than the body mode in the 7 magnetic pores studied. Given that the body modes are only observed in smaller, less magnetic pores, it is thought that strong magnetic field gradients between the larger pores and their quiescent surroundings encourage surface mode formation. An analysis of their energetics show that surface modes contain more energy (~22 kW/m^2) than body modes (~11 kW/m^2) implying surface modes may be of greater importance to the question of atmospheric heating.<br><br>Umbral Flashes, a consequence of magneto-acoustic wave propagation into the chromosphere that have been shown to raise local umbral temperatures are studied at unprecedented resolution. Calcium 8542Å spectral scans from IBIS are employed in conjunction with thermal inversions and magnetic field extrapolations to probe the small-scale dynamics of these plasma shocks. The flashes are shown to exhibit a temperature increase of ~15% compared to the umbral average, equating to a range of 600−2000 K. It is also inferred that hotter flashes form lower in the solar atmosphere due to their increased emission. The robust detection method used also detects pixels exhibiting the two-component atmosphere of shocks for the first time in intensity images. When comparing the magnetic field with the temperature enhancements, it is found that shocks formed closer to umbra centre are more efficient in raising the local plasma temperature. Two populations were found in terms of where flashes preferentially form, in contrast to previous studies, near the umbra/penumbra boundary due to the Alfvén speed gradient and near the umbral centre due to a large density gradient. The apparent motions of flashes are shown to not be dependent on the large scale magnetic field, but they are seen to move quicker in a horizontal direction towards the umbral core. 2026-10-01T16:42:46Z Text Thesis 10.17034/32639079.v1 https://figshare.com/articles/thesis/High_resolution_wave_signatures_in_the_magnetic_solar_atmosphere/32639079 All Rights Reserved