Solar oscillations in magnetic regions

by Christopher Hanson

Institution: Monash University
Department: School of Mathematical Sciences
Year: 2015
Keywords: Helioseismology; Wave propagation; Magneto-seismology
Record ID: 1047957
Full text PDF: http://arrow.monash.edu.au/hdl/1959.1/1144472


In the 50 years of helioseismology, we have gained an extensive understanding into the physical processes present within our sun. With the aid of high resolution observations and increased computational power, the current body of understanding is rapidly growing. However, there are still many questions left answered today. In this thesis, we will address two phenomena in order to shed light on their related open questions. In the first part, we will examine the scattering regimes that exist within bundles of thin magnetic flux tubes. In particular, we will address the question of how magnetic plage can absorb large amounts of wave energy and whether the resultant scattered wave field can be used to infer the magnetic field structure. The second phenomenon concerns the seismic sources that are situated within acoustic power halos and what role of the magnetic field has in enhancing these sources. In addressing the multiple scattering regime, a semi-analytical model was developed in order to model the scattering between numerous thin flux tubes situated within a stratified atmosphere. We have used a method originally designed for oceanic wave scattering, and applied it to a solar context. While to some extent this has been done in the past, we further develop the model to include the scattering of all possible modes between thin magnetic flux tubes. In doing so, we outline and address a mathematical error in the original formalism, that was not apparent until previous results were compared to recent numerical studies. Numerous case studies are then examined, ranging from the simple case of two interacting tubes, to large numbers of closely packed tubes. Various parameters are explored and the effect these have on the scattering regime is reported. Our results compare quite well with numerical and observational studies, and this model presents a significant step forward in understanding how the scattered wave field can be used to infer the internal constitution of a slender magnetic field structure. On addressing the second phenomenon, we employ the helioseismic holography technique to examine the enhanced seismic sources that are situated within the acoustic power halo that surrounds complex active regions. We examine three active regions using SDO data and apply strict statistical precautions in our analysis. The relationship between the seismic sources and the magnetic field is explored, with a strong correlation found between seismic enhancement and quasi-horizontal fields of intermediate strength. Additionally, the most intense seismic emitters (acoustic glories) were found to be located within fields very close to horizontal. The relationship between the seismic source halos and the commonly used local acoustic power maps is also explored, with large similarities reported. We found that the greatest difference between the two types of halos occurs within the high frequency (9 mHz) regime. The results of this observational study agree with other recent studies, however this study presents a significant advancement…