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標題: | 海洋暖渦對颱風強度影響的數值實驗研究 The Effect of the Ocean Eddy on Tropical Cyclone Intensity |
作者: | Chia-Ying Lee 李佳穎 |
指導教授: | 吳俊傑 |
關鍵字: | 暖渦,颱風強度,海氣交互作用, warm eddy,tropical cyclone,intensity,air-sea interaction, |
出版年 : | 2006 |
學位: | 碩士 |
摘要: | 2005年超級颶風Katrina侵襲美國紐奧良地區,重創美國經濟民生。觀測發現Katrina在經過墨西哥灣的暖水域(Loop Current)時,強度自第二級颶風快速地增強到第五級颶風。值得注意的是,除了Katrina外,無論在太平洋或大西洋上許多超級颱(颶)風,如2003年太平洋上的超級颱風Maemi及2005年大西洋上的超級颶風Rita,都被觀測到它們在經過海洋的暖渦或暖洋流(warm eddies or Loop Current)時明顯迅速增強 (rapid intensification)。這樣的快速增強過程,到目前為止是數值模式所無法完全掌握的,更遑論預報。本研究主要的目的即是討論不同的海水熱力結構(特別是海洋中存在的暖渦)對颱風強度有何重要的影響。
研究中使用一個理想的海氣耦合模式,模擬颱風在不同海洋結構中的發展。模擬結果發現,不同的海洋結構會影響到颱風所引起的海洋負回饋的強度,進而影響到颱風的最終強度。此研究同時也模擬颱風遭遇到暖渦時的反應,採用兩個回饋指數 -- FEDDY-S與FEDDY-T,來進一步地量化並探討海洋暖渦對颱風強度的影響程度。結果顯示當颱風遇到暖渦時,颱風的強度會快速增強,因為暖渦能夠提供較多的表面熱通量,且颱風所引起的海洋負回饋作用也因為暖渦深厚的混和層所產生類似絕緣體的角色(隔絕颱風與混和層下方的冷海水)而遭到抑制。 另外我們也利用大量的數值實驗及最小方差近似得到FEDDY-T與模式參數的相關性,由此並發現混和層厚度是個相當具有影響性的環境參數,其次為颱風移動速度與環境相對濕度。 研究中也討論當颱風遇到海洋冷渦時的反應,結果發現冷渦與暖渦對颱風強度影響相反但程度卻相當類似。 The rapid intensification of Hurricane Katrina along with a devastating hit to the southern states of the U.S. is a case in point to highlight the critical role that the upper oceanic thermal structure (such as the ocean eddy or Loop Current) plays in affecting the development of tropical cyclones. In this thesis, the impact of the ocean eddy on tropical cyclone intensity is investigated using a simple hurricane-ocean coupled model. Numerical experiments with different oceanic thermal structures are designed to elucidate the responses of tropical cyclones encountering the ocean eddies and the influence of tropical cyclones on the ocean. This simple model shows that rapid intensification occurs in a storm encountering the ocean eddy due to enhanced heat flux. While strong wind usually causes strong mixing in the mixed layer and thus cools down the sea surface, such a negative feedback to the storm intensity is limited at the presence of warm ocean eddy which provides insulating effect against the storm-induced mixing and cooling. Two eddy factors, FEDDY-S and FEDDY-T, are defined to evaluate the effect of the eddy on tropical cyclone intensity. The efficiency of the eddy feedback effect depends on both the oceanic structure and other environment parameters, including properties of tropical cyclone. Analysis on the functionality of FEDDY-T shows that the mixed-layer depths of the large-scale ocean and of the eddy are the two most important factors determining the magnitude of eddy feedback effect. Next to them are the storm’s translation speed and the ambient relative humidity. In contrast to warm ocean eddies, cold ocean eddies impede storm’s intensification and even reduce storm’s intensity. The impact of the cold ocean eddy is similar in magnitude but opposite in sign to that of the warm ocean eddy. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/34764 |
全文授權: | 有償授權 |
顯示於系所單位: | 大氣科學系 |
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