Air-Sea Interaction During Landfalling Tropical and Extra-Tropical Cyclones
說明
203 p
附註
Source: Dissertation Abstracts International, Volume: 76-07(E), Section: B
Adviser: Ruoying He
Thesis (Ph.D.)--North Carolina State University, 2014
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Tropical and extra-tropical cyclones represent large, discrete events that result in drastic changes to the coastal shoreline, displacement of persons, damage to property and infrastructure, and deaths each year. The ability to accurately predict these events can provide advanced warnings and dramatically reduce their impacts. Several numerical models have been developed over the past 30 years that accurately model the individual environmental conditions in which these storms develop and thrive. However, these cyclones are dependent not only on the individual environmental conditions but also the interactions and feedbacks between them. Improvement to the prediction of tropical and extra-tropical cyclones, as well as the ocean environment in which they exist, is sought through development and implementation of a coupled modeling system, known as the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model
In the first chapter, motivation and literature review is presented with the aim of demonstrating the importance of accurate prediction of the ocean, atmosphere, and wave environmental conditions in tropical and extra-tropical cyclone hindcast and forecast. Several analytical and numerical studies are researched in order to provide sufficient background into the problem, provide motivation into developing a coupled numerical model, and explain previous coupled numerical studies. Based on the existing state of knowledge, it is hypothesized that coupled modeling systems will provide improvement to the prediction of hurricane intensity, environmental states of surface waves and sea surface temperature, and atmospheric impact from precipitation distribution. This is demonstrated with 3 different tests of Hurricanes Ivan (2004), Sandy (2012), and Irene (2011)
In the second chapter, Hurricane Ivan (2004) is used as a test case for multiple uncoupled and coupled experiments into a model hindcast of the event. The methods of model coupling are presented with configurations of the uncoupled and coupled models detailed. Comparisons of simulated track, and intensity are evaluated, demonstrating improvement in prediction of the tropical cyclone intensity through coupling. The ocean and wave environments are also examined, with remote and in situ observations employed to show improvement with coupled applications. A heat budget is computed, based on the dynamics of the ocean model, drawing comparison to previous case studies cited in the first chapter that show the heat flux to the atmosphere is limited by the depth of the surface mixed layer with the ocean heat loss due to diffusion in shallower water and advection in deeper locations
In the third chapter, Hurricane and Post-Tropical storm Sandy (2012) is demonstrated as a test case in order to examine coupling impacts on a storm undergoing extratropical transition. As in the Ivan case, verification data of track and intensity are used and a strength comparison is added. An examination of the environmental variables immediately prior to landfall is conducted in order to determine the relative importance of ocean coupling during extratropical transition. It is identified that in contrast to Ivan, coupling did not provide an increase in predictability of TC intensity, most likely due to the speed of the storm. But the coupling was significant to provide accurate wave simulations
In the fourth chapter, Hurricane Irene (2011) is used as the experimental case. In this section, we demonstrate model performance through forecast (rather than hindcast) in predicting Irene's two impacts along the United States east coast. As in previous chapters, comparisons to strength and intensity will be performed. With Irene, the emphasis is shifted towards precipitation impacts, before, during, and after landfall. Precipitation analysis will be conducted using remotely observed variables of precipitation rate and intensity. Precipitation flux into the ocean will be examined in order to determine the impact on a salinity budget in the upper-ocean. Salinity cross-sections show the precipitation signature as the storm moves along the coast, which rapidly disappears under heavy wind. As in previous cases, comparison to ocean and wave environments is completed using multiple in situ data sources of 10 m wind, SLP, SST, and significant wave height
The final chapter serves to review the discussions of the previous chapters and seeks to provide a platform for future research. The utility of coupled numerical modeling is reiterated and the success of the study highlighted that showed coupling to the ocean was significant in regions of high heat content and deep mixed layer depth but coupling to a wave model was more important for faster moving TCs. Prediction of rainfall was improved when coupling to an ocean model versus without coupling. Significant improvement of the initial condition in hindcast and forecast will be sought in future research. In addition, several questions remain in improving and examining the coupled numerical solution of a tropical cyclone. Some of these questions require datasets that examine air-sea interactions in environments of intense TCs where minimal data currently exists. In addition, existing parameterizations have not been thoroughly tested in extreme wind regimes
