Internal waves are generated in the ocean by oscillating tidal flow over bottom topography such as ridges, seamounts, and continental slopes. They are similar to the more familiar surface waves, but not being constrained to move on the surface, propagate throughout the bulk of the world oceans. Internal waves transmit energy over thousands of kilometers, ultimately breaking and releasing their energy into turbulence and mixing. Where these internal waves are generated, as well as where and how they break and cause mixing, has important effects on the general circulation of the ocean, which is in turn a major component in earth's climate. As a first step in a more thorough understanding of the evolution of internal waves in the ocean, it is important to characterize their generation. The two-dimensional generation problem has been studied for four decades, with ample experimental, numerical, and theoretical results. Most of this past work has also been done using linear, inviscid approximations. However, wave generation in the ocean is three-dimensional (3D), and in many locations, nonlinear and viscous effects can be significant. Recent advances in experimental and numerical techniques are only now making the fully nonlinear, 3D generation process accessible. We utilize these new techniques to perform both laboratory experiments and numerical simulations on internal wave generation in 3D. We find that a significant component of the internal wave field generated by tidal flow over 3D topography is radiated in the direction perpendicular to the tidal forcing direction. This could lead to substantial improvements of global internal wave generation models. In addition, we have developed a new method for statistical analysis of ocean data sets, and have found large regions in the deep ocean where internal waves may not propagate. This will also have important effects on the way researchers study the propagation of internal waves, which, when propagating downward, were previously thought to always reflect from the sea floor. / text

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A parameterization is presented for turbulence dissipation due to baroclinic tide impacting on abrupt shelf topography that is supercritical with respect to the tide. The parameterization requires knowledge of the topography, stratification, and the remote forcing velocity. Upon impact, the tide cascades to higher vertical modes. Vertical internal modes that are arrested at the crest of the topography in the form of lee waves are assumed to dissipate, while faster modes are assumed to propagate away. The energy flux in each mode is predicted with topography that allows linear numer- ical solutions. The parameterization is tested using high-resolution two-dimensional numerical models of baroclinic tides impinging on an isolated shelf of various heights approximated as a step-function. The recipe is seen to work well compared to numeri- cal simulations of isolated shelves, although it consistently underestimates model flux divergence. Despite low forcing velocities having a more accurate numerical linear solution, the recipe does poorly because it does not accurately predict the modes that become trapped and dissipate. Maximum dissipation occurs when flow is on-shelf and lee waves form, indicating lee waves are the mechanism by which dissipation occurs. / Graduate / 0415

A parameterization is presented for turbulence dissipation due to baroclinic tide impacting on abrupt shelf topography that is supercritical with respect to the tide. The parameterization requires knowledge of the topography, stratification, and the remote forcing velocity. Upon impact, the tide cascades to higher vertical modes. Vertical internal modes that are arrested at the crest of the topography in the form of lee waves are assumed to dissipate, while faster modes are assumed to propagate away. The energy flux in each mode is predicted with topography that allows linear numer- ical solutions. The parameterization is tested using high-resolution two-dimensional numerical models of baroclinic tides impinging on an isolated shelf of various heights approximated as a step-function. The recipe is seen to work well compared to numeri- cal simulations of isolated shelves, although it consistently underestimates model flux divergence. Despite low forcing velocities having a more accurate numerical linear solution, the recipe does poorly because it does not accurately predict the modes that become trapped and dissipate. Maximum dissipation occurs when flow is on-shelf and lee waves form, indicating lee waves are the mechanism by which dissipation occurs. / Graduate / 0415

Graduation date: 1980 / The printing on pages with "Explanation of Figures" is very light. Best scan available.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1985. / Bibliography: leaves 76-78. / Photocopy. / x, 78 leaves, bound ill., maps 29 cm

Typescript (photocopy) / 1 v. (various paging) : ill. ; 30 cm / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1982

This thesis is concerned with the dynamics of the middle atmosphere over the southern-most continent on our planet, Antarctica. Building on previous observational and theoretical efforts to understand the dynamics of this region of the atmosphere, the work encompasses instrument improvements as well as data analysis studies of gravity waves in the lower and middle stratosphere, tides in the upper mesosphere and lower thermosphere, and short-period planetary waves in the stratosphere and mesosphere. An upgrade of the Medium-Frequency Spaced Antenna (MFSA) radar at Scott Base, Antarctica, was carried out in 2004/5 in order to ensure continued operation and enhance its capabilities to measure gravity waves. As a result, the quality of the wind measurements was greatly enhanced and the amount of data collected is now greater by a factor of approximately 15 compared with before the upgrade. Analysis of over two decades of wind velocity data from Scott Base yields a reliable climatology of the dynamics of the upper mesosphere and lower thermosphere in this area, namely the tidal oscillations and the background winds. In addition, interannual variability is assessed and periodicities of approximately 11 years and strong positive trends in tidal amplitudes are reported. Mechanisms that could explain the observed behaviour are proposed. The data are then combined with wind measurements from Halley, the longitudinal conjugate site, in order to study the zonal character of the semi-diurnal tide. Zonal wavenumber 1 and 2 waves are both found and mechanisms that could explain the generation of a wavenumber 1 component are suggested. Two further sets of MFSA radar wind measurements are used to investigate the behaviour of planetary waves with periods of between two and four days in the Antarctic middle atmosphere. Satellite temperature measurements further help to create a more complete picture of these waves. Baroclinic and barotropic instabilities, which result from shears of the zonal wind, appear to be responsible for much of the observed wave activity. In addition, a quasi-to day wave event in mid-May 2005 with unusually large amplitudes is examined and suggested to be linked to a solar proton event. Gravity wave activity over Antarctica is studied using temperature profiles obtained through the satellite radio occultation technique. Although the measurements are restricted to below 35 km altitude, high-resolution temperature profiles allow conclusions to be drawn about the seasonal, geographical, and height distribution of gravity wave activity. Mountain waves are found to be important over the Antarctic Peninsula and the Transantarctic mountains where they contribute more than 20% of the observed wave activity in the lower stratosphere. In addition, the analysis indicates the importance of critical-level filtering and Doppler-shifting.

Thesis (Ph.D.)--McMaster University (Canada), 1994. / Source: Dissertation Abstracts International, Volume: 58-06, Section: B, page: 3088. Adviser: D. L. Welch.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics, 1982. / Typescript (photocopy).