The barotropic tide dissipates a well established estimate of 2.5 TW of energy at the M2 frequency. Bottom topography is responsible for part of this dissipation, and the generation of the internal tide is also partly responsible. The fate of this energy is largely described by a cascade from large scales to small scales by non-linear wave-wave interactions where it gets dissipated. This thesis aims to investigate how the presence of mesoscale eddies (vortices) in the ocean affect the internal tide. Previous work has looked at the interaction of the barotropic tide with eddies. Krauss (1999) found that the interaction can produce a modulated internal tide, however a scaling analysis suggests that the effect may not be as strong as reported. The MITgcm is used to simulate internal wave generation by barotropic flow over topography and comparisons are made with Dr. Lamb's IGW model. Baroclinic eddies are analytically prescribed and then geostrophically adjusted also using the MITgcm. Finally, the two are combined, and the internal tide field is analysed with and without the presence of eddies of various magnitude and length scales. The results of this investigation do not find a strong transfer of energy between modes; the modal distribution of energy in the internal tide remains the same when an eddy is added. However, focusing and shadow beams of internal waves are produced in the wake of an eddy as the internal waves pass through it. The beams show very strong variations in intensity, vertically integrated energy flux can reduce almost to zero in the shadow regions and increase more than double in the focusing regions. Modal decomposition of the horizontal flow field reveals that mode 2 and 3 waves are most strongly affected by the eddies and contribute strongly to the formation of the beams. Mode 1 appears to be less affected by the eddy. The larger wavelength and faster group velocity of mode 1 supports the notion that the eddy interacts with it less.

The barotropic tide dissipates a well established estimate of 2.5 TW of energy at the M2 frequency. Bottom topography is responsible for part of this dissipation, and the generation of the internal tide is also partly responsible. The fate of this energy is largely described by a cascade from large scales to small scales by non-linear wave-wave interactions where it gets dissipated. This thesis aims to investigate how the presence of mesoscale eddies (vortices) in the ocean affect the internal tide. Previous work has looked at the interaction of the barotropic tide with eddies. Krauss (1999) found that the interaction can produce a modulated internal tide, however a scaling analysis suggests that the effect may not be as strong as reported. The MITgcm is used to simulate internal wave generation by barotropic flow over topography and comparisons are made with Dr. Lamb's IGW model. Baroclinic eddies are analytically prescribed and then geostrophically adjusted also using the MITgcm. Finally, the two are combined, and the internal tide field is analysed with and without the presence of eddies of various magnitude and length scales. The results of this investigation do not find a strong transfer of energy between modes; the modal distribution of energy in the internal tide remains the same when an eddy is added. However, focusing and shadow beams of internal waves are produced in the wake of an eddy as the internal waves pass through it. The beams show very strong variations in intensity, vertically integrated energy flux can reduce almost to zero in the shadow regions and increase more than double in the focusing regions. Modal decomposition of the horizontal flow field reveals that mode 2 and 3 waves are most strongly affected by the eddies and contribute strongly to the formation of the beams. Mode 1 appears to be less affected by the eddy. The larger wavelength and faster group velocity of mode 1 supports the notion that the eddy interacts with it less.

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

No description available.

No description available.

Space missions like Kepler have revolutionized asteroseismology, the science that infers the stellar interiors by studying oscillation frequency spectra of pulsating stars. Great advancements have been made in understanding solar-like oscillators. However, this is not the case for variable stars of intermediate masses, such asScutiand Doradus variables. By studying these stars in eclipsing binaries (EBs), model independent funda- mental parameters such as mass and radius can be inferred. On one hand, this synergy constrains the parameter space and facilitates the asteroseismic modeling, and this is shown for the Scuti type pulsating EB KIC 9851944. On the other hand, studies of binary stars must address the complexities such as mass transfer. KIC 8262223 is such an example, which consists of a mass-gaining Scuti primary and a pre-He white dwarf secondary. Some of the eccentric binary systems, the ‘heartbeat’ stars, show tidally excited oscillations. After briefly reviewing the linear theory of tidally forced stellar oscillations, we study the tidal pulsating binary KIC 3230227 and demonstrate that both amplitude and phase can be used to identify the tidally excited pulsation modes. We also discuss the variability of a Slowly Pulsating B-star KOI-81 and a Cataclysmic variable KIC 9406652. In the second part of this dissertation, we apply Bayesian statistics to some problems in binaries and asteroseismology with the help of packages BUGS and JAGS. Special attention is paid to the inverse problems (tomography) encountered in studying the double-line spectroscopic binaries.

The relationship between nutrients and community structure is poorly understood in open-coast habitats. I created a system of artificial tidepools, of identical age and physical dimensions, at two sites that differed in wave exposure, and manipulated nutrient levels and the abundance of herbivores. Using these unique field mesocosms, I explored the role of changes in nutrient dynamics and tested two predictive models of community structure in a rocky intertidal community. I modified a simple food-chain model to include the effect of hydrodynamics on nutrient delivery rates and herbivore foraging efficiency. Field experiments demonstrated that nutrients had strong effects on the abundance and productivity of seaweeds. Algal productivity was negatively influenced by herbivory, contrary to model predictions, because species with the potential to increase growth rates when given additional nutrients were virtually eliminated in the presence of herbivores. The effects of both nutrients and herbivory varied in a manner consistent with predicted effects of hydrodynamic forces. Contrary to simple food-chain models, herbivores did not respond to nutrient additions. I assessed nutrient dynamics during low tide, demonstrating that nutrients were rapidly depleted from tidepools. I also examined variation in nutrient uptake rates relative to the experimental treatments described above, for both whole pools and on a biomass-specific basis. Nutrients were almost always removed from pools at the same rate dispensers added them. Uptake rates were significantly correlated with the abundance of fleshy seaweeds. Synthesizing the results of these and other studies, I proposed that the abundance of tidepool seaweeds can be modeled as a function of pool volume, degree of tidal isolation, water flow at high tide, and herbivory. I tested the predictions of a functional group model and evaluated the validity of equating physical and biological disturbances by examining algal diversity and abundance patterns in tidepools along gradients of potential productivity, herbivory, scour and wave exposure. The abundance of functional groups varied along environmental gradients, but not always in a manner consistent with predictions. I suggested that physical and biological processes must be modeled separately, and that better operational definitions of environmental potentials will aid in development of these models. / Graduation date: 1999

Thesis (M.Tech.)--Cape Technikon, 1996. / Bibliography: leaf 111-121. Also available online.

Internal tide is generated in the interface of density stratification by some hydrodynamic disturbance. The major mechanisms are borotrophic tidal current oscillated at the edge of the continental shelf, submarine canyons, ridges or sills. The resulting disturbance generated has the same motion cycle of tidal period. There were internal tides reported in the Kaoping Submarine Canyon. The generation sites and mechanisms, however, are not clear. This study analysis four cruises of field observed data using ship mounted ADCP and CTD, and moored temperature strings and current meters. The results showed: (1) The phase of M2 tidal current increase toward the canyon head, with minimum value at the canyon mouth. This result implies that the internal tide was generated near the canyon mouth and propagated up canyon with the thermocline decreasing toward the shallower water. (2) The internal tide generated at the canyon mouth propagated, through some mechanisms, at the upper layer density interface about 150m instead of beaming near the bottom layer where the current and topography interact. (3) The vertical variations of tidal ellipse and phase based on bottom mounted ADCP support the results of ship mounted observations, the internal tidal energy propagates near the interface of 150m below the surface.

In order to understand tidal circulation and oceanic current for the seas around Taiwan, this study use a baroclinic unstructured grid model to build a high resolution model. This model use semi-implicit method to solve the dynamic of ocean movement and larger time step can be used to calculate. Unstructured grid can be used to resolve complex coastline and variation of depth. TaiDBMv6 depth data were chosen to describe the depth distribution and grid mesh size were determined by local depth, minimum mesh size is about 0.75 minutes, and maximum 13 minutes. Tidal boundaries use 8 constituents derived from FES2004 and calibrated with 34 tide station records. Data of 2009 were used to evaluate the model results. The average of all station root mean square error was 10.1 cm. Station at east side of Taiwan have smaller errors, which almost lower than 5 cm. The maximum error can be found inside Taiwan Strait, about 25cm, mainly caused by lack of depth data near the coastal area. For oceanic current model, GFS and NFS-MC CWB wind forecast were used as meteorology input. Initial fields and boundary condition are derived from HYCOM results. Nudging of salinity and temperature also were used to stabilize the model. Transport of Kuroshio of 2009 is about 17.0¡Ó3.2Sv. Maximum value is about 28.6Sv, occurred in summer. Minimum value is about 8.3Sv, occurred in winter.