臺灣博碩士論文加值系統

本論文研究主要係藉由分析實測、遙測、及數值模式資料探討西太平洋中尺度渦漩的結構與傳播行為及其對西方邊界流（黑潮）的影響。
世界海洋環流實驗（WOCE）於台灣東邊的錨碇測線（PCM-1）顯示黑潮的通量與西太平洋渦漩有著密切的關係。本研究先以衛星測高儀與XBT資料追蹤PCM-1觀測期間最大事件的低壓渦漩（eddy 9410L），藉由經驗正交函數（EOF）分析結果重建eddy 9410L的結構，並指出EOF的第二模扮演使渦漩結構傾斜的角色，其西向與北向的傳播速率分別為6.5 km/day 與7.5 km/day。接著以二維之QG數值模式探討9410L的傳播過程，模式結果指出渦漩的西向與北向的傳播速率隨緯度的增加而降低，且L/Rd （L:渦漩直徑，Rd:Rossby deformation radius）的比例亦影響其傳播速率，在無背景流場影響下，低壓渦漩西向與北向的傳播速率分別為2.5~4.8 km/day與0.3~3 km/day，在加入北向6km/day背景流場下，低壓渦漩西向與北向的傳播速率則分別為2.8~5.2 km/day與1.8~7.6 km/day，由此得之eddy 9410L向北傳播應係受到西太平洋大尺度北向流場的影響所致。
為蒐集更多渦漩資料並探討渦漩與黑潮交互作用的過程，本研究進一步分析美國海軍實驗室（US Naval Research Laboratory）所發展具備資料同化功能並實際運作中的北太平洋三維數值模式（NPACNFS）於1999.7.1~2002.7.30的結果。模式結果中眾多渦漩的結構，呈現了與eddy9410L類似的結構，但渦漩西傾的現象會因緯度不同而有所差異，緯度越低西傾現象越明顯，且溫度最大變異值的位置也隨緯度變低而深度越深。
於模式計算期間黑潮通量台灣東側的平均值約為25 Sv，季節變化為6 Sv。模式結果的平均值以及季節性變化皆略大於WOCE PCM-1的實測結果（約21及 4Sv），其間歇性約100天週期的震盪則與PCM-1的觀測相符，但模式的振幅似乎略小於PCM-1的10 Sv。因模式的計算期間並非與WOCE同步，故此些微差異應屬正常。
利用EOF分析126˚E以西區域的動力高度，可明顯看出EOF第一模（解釋變化總量的57%）代表季節性變化（季節模），第二模（13%）代表渦漩運動的影響（渦漩模），向西傳播的渦漩主要從20˚N的位置與黑潮產生交互作用，引發台灣東南方的海域水團運動，進而影響黑潮的流軸及通量改變，西向傳播的高壓渦漩使部份黑潮偏離主軸東向蜿蜒而降低北向通量，低壓渦漩則引進黑潮東側的海水使通量增加。
速度場的EOF分析指出運動結構有隨深度逐漸轉變的現象，上層變化以季節模為主，渦漩模的結構則於深度200m附近為主導的速度結構，再進一步以SVD分析動力高度場與各層速度場最大相關的結構，顯示動力高度場的前兩模即為兩種資料的相關結構，速度場季節性變化集中於上層，但渦漩運動則在各深度呈現近乎一致的分佈，故在混和層以下扮演了比季節性變化更重要的角色。

The study is focused on the mesoscale eddies in the western Pacific: their structure, behavior of propagation, as well as interaction with western boundary current (Kuroshio), utilizing the data from observations, remote sensing and numerical model.
The results from World Ocean Circulation Experiment (WOCE) volume transport monitoring line east of Taiwan (PCM-1) indicate that eddies on 100 day time scale can significantly affect the Kuroshio transport. In this study, we trace the largest cyclonic eddy event, eddy 9410L, during the observation period of PCM-1 using altimetry and XBT data. The temperature structure of 9410L is reconstructed according to the resolved first and second modes from Empirical Orthogonal Function analysis (EOF). The first mode of EOF reveals the symmetric component of vertical structure, and the second mode reflects the tilting component. The observed northward and westward propagation speed of 9410L is 6.5 and 7.5 km/day respectively. A quasi-geostrophic (QG) model is applied to examine the propagation behavior of the eddy. Model results suggest that the propagation speed depending on the ratio of L/Rd (L : radius of eddy，Rd : Rossby deformation radius), and in general, decreases with increasing latitude. For a typical cyclonic eddy without background flow, the propagation speed is 2.5~4.8 km/day westward and 0.3~3 km/day northward respectively. Adding a 6 km/day northward background current, the propagation speed is advanced to 2.8~5.2 km/day westward and 1.8~7.6 km/day northward respectively. We therefore conclude that the large scale western Pacific northward flow field could be responsible for the observed northward propagation of 9410L.
In order to find the general characteristics of the eddies and their influences on the Kuroshio, we further analyzed the 3-year (Jul. 1, 1999 ~ Jul. 30, 2002) model results from the North Pacific Ocean Nowcast/Forecast System (NPACNFS), an operation model with satellite and in situ data assimilation developed and operated by the US Naval Research Lab (NRL). The basic (symmetric) structure of numerous eddies from the model results are similar to that of eddy 9410L, the modification (tilting), however, varies with location of the eddy. In general, eddies in the lower latitude show more tilting and the temperature anomalies extending to deeper layer.
Over this 3-year period, the mean transport of Kuroshio is about 25 Sv with seasonal variation of 6 Sv, both of which are slightly larger than those of WOCE PCM-1 measurements (about 21 and 4 Sv). The fluctuations of 100-day time scale are similar to that of PCM-1, however, the model’s amplitude seems to be smaller. Since the measurements of PCM-1 and model computation are not synchronized, the small difference of these two data sets is therefore falling within the generally acceptable range.
Application of EOF to the model dynamic height west of 126˚E reveals that the first mode (explains 57% of total variance) represents the seasonal oscillations (seasonal mode) and the second mode (13%) the influence from eddies (eddy mode). The westward propagating mesoscale eddies typically arrive at 20oN and interact with Kuroshio. The process causes the water mass southeast of Taiwan moving with the impinging eddies, deflects the axis of the Kuroshio, and changes the volume transport. An anticyclonic (cyclonic) eddy will induce a cyclonic (anticyclonic) tendency to the north and cause a decrease (increase) of the Kuroshio transport east of Taiwan.
Results from EOF of the model velocity field at each level show a structure transition varying with depth. The variation in the upper ocean is dominated by the seasonal oscillation, while the deeper layer (below 200 m depth) is influenced more by eddies. We further applied Singular Value Decomposition analysis (SVD) to both dynamic height and velocity field at each level. The results show that the first two EOF modes of dynamic height are also the relevant SVD structures. In addition, the seasonal oscillation of velocity field is basically confined to the upper ocean, but the eddy motion can be found in all level with similar amplitude. We therefore conclude that the eddy mode plays a more important role than the seasonal mode below the mixed layer.

謝誌 i
目錄 ii
圖目錄 iv
表目錄 vi
摘要 vii
Abstract ix
第一章、序論 1
1.1 前言 1
1.2 研究區域與地理環境 2
1.3 文獻追溯 4
1.3.1渦漩動力研究與觀測 4
1.3.2渦漩沒入灣流之研究 7
1.3.3渦漩對黑潮台灣段通量的影響 8
1.4研究目的 9
第二章、渦漩eddy 9410L 之溫度結構與運動行為 12
2.1 前言 12
2.2 資料 12
2.2.1衛星測高儀(TOPEX/Poseidon Altimetry) 12
2.2.2 CTD與XBT 18
2.3 分析結果 19
2.3.1動力高度(DH)計算 19
2.3.2動力高度(DH)與海面高度異常值(SSHA)之比較 22
2.3.3 Eddy 9410L溫度結構重建 25
2.4 數值模擬 29
2.4.1模式 29
2.4.2數值實驗 30
2.5 討論與小結 40
第三章、三維數值模式 46
3.1 前言 46
3.2 模式介紹 46
3.3 模式與觀測資料之比較 47
3.3.1 海面高度(SSH) 47
3.3.2 模式動力高度 vs. T/P_SSHA 52
3.4小結 56
第四章、西太平洋渦漩場分析- Cases study 58
4.1 前言 58
4.2 渦漩傳播 58
4.3 渦漩結構 65
4.4 討論與小結 71
第五章、渦漩與黑潮之交互作用 73
5.1 前言 73
5.2 黑潮ETC通量 73
5.3 EOF分析 76
5.3.1 動力高度場分析(dh_EOF) 76
5.3.2 速度場分析(uv_EOF) 79
5.3.3 溫度場分析(t_EOF) 82
5.4 SVD 分析 ― 動力高度 vs. 速度場 85
5.5 討論與小結 89
第六章、結論 92
參考文獻 95
附表一 99
個人著作表 100
附件一 Structure and Propagation of a Large Cyclonic Eddy in the Western North Pacific from Analysis of XBT and Altimetry Data and Numerical Simulation
附件二 Eddies and Kuroshio Transport East of Taiwan
附件三 Variability of Subtropical Circulation in Western North Pacific

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