Semi-empirical Studies Of Solar Supergranulation And Related Phenomena

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Semi-empirical Studies Of Solar Supergranulation And Related Phenomena

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Title: Semi-empirical Studies Of Solar Supergranulation And Related Phenomena
Author: Williams, Peter Edward
Abstract: In recent years, solar observations have moved from ground-based telescopes to observatories on Earth orbiting satellites, such as SOHO. They provide us with a clear and uninterrupted view of the solar disk. One instrument upon SOHO, the Michelson Doppler Imager (MDI), has proved fruitful in providing not only important information of the solar photosphere but, in combination with helioseismic methods, a method for probing the solar interior. This dissertation discusses current investigations by myself and my collaborators into surface manifestations of convection phenomena, using Doppler velocity data from MDI and produced from computer simulations. The Doppler data reveal convection cells much larger than the granulation seen easily by optical telescopes. These 'supergranules' originate deeper within the convection layer than the granules and, like their smaller counterparts, are heavily influential in structuring the magnetic field and subsequently play an important role in controlling aspects of the solar activity cycle. My work presented in this dissertation shows that the supergranulation pattern seems to rotate faster than the surface plasma. It has been suggested that the pattern is driven by wave-like phenomena, but instead we find the reason is a geometric effect with respect to the observer. We further find that supergranules are also responsible for observed corrugation features on the solar surface, which previously had been interpreted as Rossby wave hills. We extend our convection spectrum and Doppler map production simulations to include axisymmetric flows such as differential rotation, which contribute to the evolution of the velocity field. These models assist in understanding how such large-scale surface flows influence the surface motions of supergranules. Lastly, I describe the construction of a numerical experiment to study the influence of a 'giant-cell' velocity field on the supergranule pattern. Such non-axisymmetric flows would further contribute to supergranule advection and the results of such experiments may assist in the observation of these hitherto elusive 'giant-cells'.
Date: 2008-09-17
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