The mixing mechanism of South African cumulus congestus clouds is investigated using a combined observational and modeling approach. The experimental data consists of aircraft measurements collected in developing cloud towers near Nelspruit on three case study days. The observations are analyzed to determine the source regions of the entrained air. The mixing processes are simulated using both axially and slab symmetric cumulus models with very high spatial and temporal resolutions. The simulated clouds have a structured organization with small scale features such as in-cloud downdrafts. The mixing processes are examined by analyzing the time variation of dynamic and thermodynamic quantities along computed parcel trajectories. / Both observations and simulations indicate that most of the entrainment occurs at the cloud top. Evaporative cooling causes downdrafts that transport highly diluted air from the cloud top down to lower levels. The trajectory analysis shows that the penetrative downdrafts are also affected by pressure perturbations. / In the presence of wind shear the downshear sides of the clouds become more diluted, cooler and have stronger downdrafts. The asymmetric organisation is attributed to turbulent exchange of horizontal momentum at the cloud top.

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The Magellanic Clouds have long provided a rich celestial laboratory for many astrophysical research programmes. Their location relatively close to the Earth and away from the plane of our Galaxy has made them a natural target for Southern Hemisphere ground-based instrumentation. Likewise, the continuing quest for images of the Clouds with higher dynamic range and improved angular resolution has driven a continual improvement in instrumentation across a range of wavelength bands. The cornerstone of this thesis is a study of selected sources in the Magellanic Clouds. The sample was chosen from the 843MHz Molonglo Observatory Synthesis Telescope survey of the Clouds, based on the existing knowledge of each source, its flux density and angular extent. This sample was used to explore observational and analysis techniques with the Australia Telescope Compact Array in order to better determine the nature of these objects and to identify those sources worthy of further study. This work highlights many pertinent issues associated with the correct classification of sources when only a limited amount of data is available. These issues led directly to the development of a more systematic approach in the classification of the Large Magellanic Cloud source sample, detailed for the first time in this thesis. Two supernova remnants in the Small Magellanic Cloud were studied in detail. The Australia Telescope images of 1E0102.2-7219 revealed, for the first time, the radio structure of this young oxygen-rich supernova remnant, and allowed a detailed comparison with existing optical and X-ray data to be undertaken. The comparisons presented in this thesis and in an earlier publication have prompted exciting new X-ray observations at unprecedented angular resolution. The second, 0101-7226, studied as part of an international collaboration, has a shell morphology at radio wavelengths but no associated X-ray emission and is therefore something of an enigma.

Thesis (Ph.D.)--Rochester Institute of Technology, 2007. / Typescript. Includes bibliographical references (leaves 173-175).

Thesis (Ph.D.)--York University, 2006. Graduate Programme in Earth and Space Science. / Typescript. Includes bibliographical references (leaves 188-201). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR19810

Thesis (Ph. D.)--University of Nevada, Reno, 2007. / "August, 2007." Includes bibliographical references (leaves 116-119). Online version available on the World Wide Web.