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Wind Effects on the Temperature Variation of Vortex Street in the Kuroshio-Green Island System
|Authors: ||Ho, Chia-Ying|
|Contributors: ||NTOU:Department of Marine Environmental Informatics|
Green-Island;Kuroshio;Vortex;Aspect ratio;Dimensionless width
|Issue Date: ||2020-01-20T06:20:38Z
|Abstract: ||本研究是利用高解析度Bryan-Cox-Semtner（1974）的海洋環流模式（Oceanic General Circulation Model, OGCM）來探討當黑潮流經到綠島時所產生的渦旋現象。所使用的地形為海洋學門資料庫所提供的真實海底地形，水平解析度為500公尺，垂直方面共有76層。模式設定了4種不同的流量及4種不同的風來探討不同的雷諾數和風應力對於綠島尾流的影響。結果發現當黑潮主軸撞擊綠島時，島嶼後方會產生低溫的水團，溫度降幅約0.6度，擺動情形與卡門渦街類似，擺動週期為15小時，島後渦旋長寬比約為1.95 ~ 2.04，無因次寬比值約為1.2 ~ 1.48，St值約為0.1697。然而在把模式邊界流量減少時，發現島後擺動現象卻消失了，但島後依然還是有低溫水團的產生。當模式吹西南風時，溫度的降幅約為0.8度，此時島後渦旋長寬比約為2.47 ~ 2.96，無因次寬比值約為1.02 ~ 1.33。相較之下在吹東北風時，則溫度的降幅僅為0.4度，此時島後渦旋長寬比約為1.14 ~ 1.7，無因次寬比值約為1.23 ~ 1.66。而當把兩種風加大風速後，渦街現象也隨之消失。|
In this study, the Bryan-Cox-Semtner (1974), a high-resolution Oceanic General Circulation Model, is used to simulate the vortex streets generated by Kuroshio flows past the Green Island. A real topographic is adopted for the model dataset from Ocean Data Bank. The horizontal resolution in x-y direction is 500-meter and there are 76 levels in the vertical direction. The model is set to different conditions, such as four different boundary fluxes and wind stresses, to study these factorial effects on the vortex streets and Reynold number. The model results show that a low temperature water mass is usually generated behind the Island when the Kuroshio Current impacts on the Green-Island. Temperature cooling degree of the upwelling water in the wake is about 0.6°C. The wake is similar to the von Kármán vortex street, and the cycle of its oscillation is about 15 hours. Aspect ratio of the vortex train is in range from 1.95 to 2.04 and its dimensionless width is between 1.2 and 1.48; Strouhal number is 0.1697. However, the wake still disappears when the model boundary flux is reduced, but also have a low temperature water mass behind the Island. During the blowing southwest winds, the temperature cooling degree of water upwelled in the wake is about 0.8°C. Aspect ratio of the vortex train is in range from 2.47 to 2.96 and its dimensionless width is between 1.02 and 1.33. When it prevails the northeast winds, temperature cooling degree of water upwelled is about 0.4°C, the aspect ratio of the vortex train is range from 1.14 to 1.7 and its dimensionless width is between 1.23 and 1.66. Finally, after increasing the speed of the two winds, the vortex streets are also vanished.
|Appears in Collections:||[海洋環境資訊系] 博碩士論文|
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