Browsing by Author "John M. Morrison, Committee Member"

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Analysis and Modeling of Wave-current Interaction
(2006-11-03) Liu, Huiqing; Lian Xie, Committee Chair; Gerald S. Janowitz, Committee Member; Leonard J. Pietrafesa, Committee Member; John M. Morrison, Committee Member
The main task of this study focuses on studying the effect of wave-current interaction on currents, storm surge and inundation as well as effects of depth-induced wave breaking, wind field and current on waves by using numerical models. The results show that it is important to incorporate the wave-current interaction effect into coastal circulation, storm surge and inundation models. At the same time, it should consider effects of depth-induced wave breaking, wind field, currents and sea surface elevation in prediction of waves. Specially, we found that: (1) Depth-induced wave breaking plays an important role in wave field in shallow water areas; (2) To more properly model the hurricane induced wave field, it is important to consider the asymmetric structure of the hurricane wind field, the changes in the hurricane translation time history, and the incorporation background wind field into hurricane wind field; (3) For SWH, it will be decreased when waves propagate in the following current direction. On the other hand, current will increase the SWH when waves propagate countercurrent direction. The change of wave propagation direction after crossing Gulf Stream depends not only on refraction, but also on others (e.g. trap waves effect). (4) It is important to introduce wave-current effects into any storm surge and inundation prediction modeling system. Specially, the consideration of wave-induced wind stress, bottom shear stress, and 3-D radiation stress in storm surge and inundation modeling can significantly improve the correctness of the prediction.
Biochemical Analysis of Diel Vertical Migration in the Red Tide Dinoflagellate Karenia brevis
(2007-02-28) Schaeffer, Blake Allen; Daniel Kamykowski, Committee Chair; John M. Morrison, Committee Member; Gary J. Kirkpatrick, Committee Member; Hosni M. Hassan, Committee Member
Many laboratories have solely used the Wilson isolate to characterize the red tide dinoflagellate species Karenia brevis. Recent work has provided new isolates from different geographical locations. Prior to detailed biochemical investigations, laboratory studies were conducted on ten different isolates representing geographical locations around the coast of Florida. The investigation of the physiological parameters for the ten different isolates provided a foundation for the proper selection of a single isolate that would closely represent the species in the field. Each isolate was capable of a range of responses with primary dependence on cell counts within the cultures. Evidence suggests that either carbon limitation or bacterial negative feedback caused changes in the physiological parameters as cell counts increased. The Apalachicola isolate was selected for further biochemical investigations because it was representative of the group response. A nutrient-replete intermediate-light mesocosm experiment investigated the taxis patterns, and the biochemical composition of vertically migrating K. brevis populations. This experiment confirmed the internal biochemical status of the cell controlled migratory behavior, growth and reproduction. Young cells fixed carbon at the surface while older cells limited vertical migration toward the middle depth in anticipation of cellular division. The cells were capable of performing complex lipid control during vertical migration. Quick turnover of these lipids indicated K. brevis was more than capable of taking advantage of changing physical conditions. Finally, nutrient replete and deplete mesocosms investigated how K. brevis responded to field-simulated high light conditions. Results from high light and nitrogen-limited exposure suggested K. brevis may utilize the benthos by minimizing exposure to oxidative stress and as a nitrogen source supplied from benthic pore-water flow in permeable sediments. High light also caused K. brevis to increase toxin concentrations while decreasing its sterol lipid class concentrations. This response caused K. brevis to be more toxic at particular times of the day. Data from this experiment led to the conclusion that cell division yielded unequal daughter cells.
Cape Fear River Estuary Modeling System
(2008-02-28) Xia, Meng; Leonard J. Pietrafesa, Committee Member; Lian Xie, Committee Chair; Daniel L. Kamykowski, Committee Member; John M. Morrison, Committee Member
The Cape Fear River Estuary (CFRE) region is one of the coastal regions facing frequent threats from tropical cyclones. It is also an important nursery for juvenile fish, crabs, shrimp, and other biological species. Thus, predicting the physical responses of the CFRE system to extreme weather events is important to the protection of life and property and ensuring the economical well beings of local residents. In this study, the Princeton Ocean Model (POM) is used to simulate the storm surge circulation in the CFRE and adjacent Long Bay and Onslow Bay. The Environmental Fluid Dynamic Code (EFDC), an estuarine and coastal ocean circulation model, is also used to simulate the salinity plume and tracer plume distribution and particle trajectory in the vicinity of the mouth of the Cape Fear River Estuary (CFRE). The effects of astronomical tide, river discharge and wind on the CFRE salinity plume and tracer plume, particle trajectory were investigated. The comparison among the plume structure, particle trajectory, and the passive tracer structure is discussed. To better simulate the plume structure in Cape Fear River Estuary (CFRE), we also test the sensitivity of the EFDC model to the choice of grid resolution, advection scheme, and external forcing.
Interannual Variability of Climatology and Tropical Cyclone Tracks in North Atlantic and Western North Pacific
(2006-05-01) Yan, Tingzhuang; Lian Xie, Committee Chair; John M. Morrison, Committee Member; Fred H. M. Semazzi, Committee Member; Leonard J. Pietrafesa, Committee Member
The spatial-temporal variability of tropical cyclone tracks and their possible association with tropical cyclone landfall frequency along the United States East Coast and China East Coast are studied using Principle Component Analysis of tropical cyclone Track Density Function (TDF). Results show that North Atlantic (NA) hurricane TDF is strongly modulated by El Niño-South Oscillation, the tropical Atlantic SST dipole Mode (DM), North Atlantic Oscillation and Arctic Oscillation. Dominant Modes of Western North Pacific (WNP) typhoon TDF demonstrate strong correlation with spring and winter snow cover (SC) over the Qinghai and Tibetan Plateau (QTP). Results provide a foundation for the construction of statistical models, which project the annual number of tropical cyclone landfall along the East Coast of the United States and the coast of China. Analysis for 1990 and 2004 NA hurricane seasons revealed that the substantial variability of tropical Atlantic SST DM is a dominate factor affecting the hurricane track patterns. Study for 1978 and 2001 typhoon cases in the WNP demonstrated that the QTP SC was responsible for the differentiation in the number of landfall typhoon events in the WNP. A schematic diagram was proposed to illustrate the linkage between the DM and the NA hurricane track patterns. Accumulated gain or deficit in the surface radiation associated with the QTP SC imposes a long memory in the East Asian climate system. Variations in heat budget change the large-scale zonal circulation and further modulate the seasonal position and strength of East Asian subtropical high. A possible physical link to connect the QTP snow cover and the WNP typhoon track patterns was therefore proposed.