臺灣博碩士論文加值系統

本研究使用歷史水文資料(1986~2010)及海研三號的六個航次資料，以Thorpe scale及Parameterization方法中的Strain和Shear間接估算密度渦流擴散係數(Kρ)及紊流動能消散率(ε)，研究台灣東南海域紊流特性之時空分佈。首先篩選出研究範圍內(21.5~22.6°N，120.85~123°E)符合設定條件的730個水文剖面﹐分析方法以Parameterization of Strain方法為主，搭配QuikSCAT衛星提供的風場資料，分別對混合層厚度、風應力、溫度、流速、地形等，影響紊流混合的因素做分析及統計，探討造成上層海洋及底層邊界紊流混合變化的機制，並進一步深入討論該區域黑潮所造成的紊流混合特性，利用六個航次CTD及LADCP資料，分別沿著21.9°N、22.05°N、22.2°N三條測線，針對黑潮通過蘭嶼前後及流域內的垂直擴散係數變化做分析討論 。
　　三種估算方法當中，以Parameterization方法計算結果數據比較穩定，平均值較不會有偏大或偏小的情形發生，適合用在觀察大範圍現象的紊流混合分佈情形。經由歷史CTD資料統計分析，結果顯示上層海洋邊界層(水深30~200公尺)造成紊流混合季節的變化可以分為兩個部分：其中台灣東岸受到黑潮流域(121.3~122°E)的入侵影響下，造成此區域紊流混合增強現象，並且會隨著黑潮主軸的季節性擺盪造成空間上的變化；在遠離黑潮流域的區域(> 122°E)紊流混合主要是受到風應力影響，其中常發生強烈紊流混合的區域為北呂宋海槽、南縱海槽北方、蘭嶼南方及北方處。底層海洋邊界層(海底方100公尺)影響紊流混合的主要因素為地形變化，導致海流受到地形阻擋及抬升作用產生混合，其強烈紊流混合分佈在地形坡度上。受到黑潮影響下(水深0~200公尺)的Kρ約為10-4~10-2 m2s-1之間，而在鄰近的西太平洋及南海海域呈現較弱紊流混合，證實黑潮流域內的確會造成增強紊流混合，當黑潮流經台灣東岸與蘭嶼(22.05°N)之間時，由於此處地形為一個海槽地形，海水受到擠壓導致流速增強，可能造成紊流混合強度伴隨著增強。此外，黑潮主軸主要影響紊流混合的深度為大於300公尺，而在黑潮(邊緣)鋒面會增強剪切強度，影響深度為0~200公尺之間。

This study is focused on the temporal and spatial variations of turbulent mixing in the seas off southeastern Taiwan. Historical hydrographic data of 1986 ~ 2000 and in-situ data from six cruises were used to estimate indirectly vertical eddy diffusivity (Kρ) and turbulent kinetic energy dissipation rate (ε) by means of three methods, that is, Thorpe scale method and parameterization method with shear and strain values. Based on the 730 CTD profiles which were selected to meet the criteria in the study region as well as the QuikSCAT satellite-derived winds, a number of factors such as mixed-layer depth, wind stress, surface-layer temperature, current speed and bottom topographies were investigated about their influence on the turbulent mixing of upper oceans and bottom boundary layer. The role of Kuroshio on the turbulent mixing of this region is further explored. The CTD and LADCP data from six cruises were divided into three transects, i.e., along 21.9°N, 22.05°N and 22.2°N, to investigate variations of eddy diffusivities induced by the Kuroshio with and without the interference of the Lanyu Island.
　　Among the three methods examined in this study, the parameterization method showes the most satisfactory result whose mean value is stable for the large scale evaluation of turbulent mixing distribution. Analysis of historical CTD profiles shows that seasonal variations of turbulent mixing in the upper water column (30 ~ 200 m depth) can be classified into two different parts. When the Kuroshio intrudes into the area off eastern Taiwan (121.3 ~ 122 °E), turbulent mixing is enhanced and its spatial variation is consistent with the seasonal migration of Kuroshio. In the area farther from the Kuroshio (east of 122 °E), the dominant factor affecting turbulent mixing is the wind which exerts great influence in northern Luzon Strait, the north of Southern Longitudinal Trough, and southern and northern parts of Lanyu Island. Turbulent mixing in the bottom boundary layer (&;lt; 100 mab) has close correlation with the bottom topography. At steep slopes currents will be forced to rise which will cause strong mixing. Under the influence of Kuroshio Current (0 ~ 200 m depth), Kρ can reach 10-4~10-2 m2s-1, which is much larger than those in the open ocean of the Western Pacific and South China Sea, evidencing the role played by the Kuroshio in enhancing the turbulence. Turbulent mixing could also be greatly enhanced when the Kuroshio flows through the channel between Lanyu Island and Taiwan, causing the current speed to increase. The depth that Kuroshio Current exerts marked influence on the turbulent mixing is 300 m or deeper, and the vertical shear is increased at the front of Kuroshio, affecting the turbulence in 0 ~ 200 m depth.

論文審定書 i
誌 謝 ii
中文摘要 iii
英文摘要 iv
目 錄 vi
圖 目 錄 viii
表 目 錄 x
參數及符號 xi
第一章、緒論 1
1.1 前言 1
1.2 研究目的 4
第二章、使用儀器及航次資料 5
2.1 儀器介紹 5
2.1.1 CTD 水文資料量測 6
2.1.2 下放式聲學都卜勒流剖儀 6
2.2 航次資料 10
2.2.1 研究區域範圍 10
2.2.2 三測線航次 10
2.2.3 南海及西太平洋航次 11
2.3 其他資料 23
2.3.1歷史水文資料 23
2.3.2 風應力 24
第三章、資料處理及分析方法 26
3.1 CTD資料處理 26
3.2 LADCP資料處理 27
3.3.1 LDEO處理軟體原理 27
3.3.2 LDEO處理軟體所需資料 28
3.3 Thorpe scale method 34
3.4 Parameterization 37
3.4.1 Parameterization計算步驟−【剪切譜】39
3.4.2 Parameterization計算步驟−【應變譜】42
第四章、結果與討論 44
4.1 三方法比較 44
4.2 紊流混合機制 52
4.2.1 水文特性 53
4.2.2 上層海洋邊界層 54
4.2.3 底部邊界層 58
4.3 黑潮流域內紊流混合現象 75
第五章、結論 97
5.1 三方法的比較 97
5.2 紊流混合機制 97
5.3 黑潮流域內變化 98
參考文獻 99

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