學位論文
Permanent URI for this collectionhttp://rportal.lib.ntnu.edu.tw/handle/20.500.12235/73900
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Item 台灣周邊海域海流之數值研究(2008) 辛宜佳; Yi-Chia HsinA multiple grid-size nesting ocean model system is developed in this work to perform studies on the variations of the flow in the Taiwan Strait and the Kuroshio east of Taiwan. The transport in the Taiwan Strait is studied using the East Asian Marginal Seas (EAMS) model. Three model experiments using different wind data sets (ERA40, NCEP Reanalysis version 2, and QuikSCAT/NCEP blend wind) were performed. Model experiments suggested that the best simulation is achieved when the model is driven by the QuikSCAT/NCEP blend wind forcing. Involving the strong wintertime southward flow events in the Taiwan Strait, the annual averaged modeled transports through the Taiwan Strait is 1.09 Sv (1 Sv=106 m3/s). The result suggests that shipboard Acoustic Doppler Current Profiler (sb-ADCP) observations are biased toward estimates in summer and fair weather since bad weather during the winter northeast monsoon often prevents seagoing observations. Linear regression lines are also proposed to give simple relations between transport and wind stress for roughly evaluating the transport through a known wind stress value. The spatial and temporal variations of the Kuroshio east of Taiwan are investigated using model outputs, surface drifter trajectories, satellite-based altimetric data, and wind data. From the simulation of the EAMS model over a span of 24 years from 1982 to 2005, the variability of the Kuroshio east of Taiwan is studied in detail. Between 22 and 25°N, the mean state and variability of the Kuroshio, such as the two paths observed in the trajectories of surface drifters southeast of Taiwan and the branching of the Kuroshio northeast of Taiwan, are well reproduced by the model. Southeast of Taiwan, the Kuroshio is mostly in the top 300 m in the inshore path but extends to 600 m in the offshore path. Northeast of Taiwan, the Kuroshio follows the shelf edge in the East China Sea, but sometimes branches along a path south of the Ryukyu Islands. The latter path often meanders southward, and a significant portion of the Kuroshio transport may be diverted to this path. The Kuroshio extends from the coast to 123°E ~ 123.5°E between 22°N ~ 25°N with currents reaching a depth of 1000 m at some latitudes. The Kuroshio transports averaged over five sections east of Taiwan are 28.4 ± 5.0 Sv and 32.7 ± 4.4 Sv with and without the contribution from the countercurrent, respectively. Using satellite data and the Seas Around Taiwan (SAT) model simulation, the intra-seasonal variation of the Kuroshio southeast of Taiwan is further studied. Superimposed with the main stream of the Kuroshio, two intra-seasonal signals longer than 2 weeks are revealed in the study region, 20 ~ 30 days and 40 ~ 90 days. The variation of 20 ~ 30 days is only significant between Taiwan and the Lan-Yu Island. Amechanism is proposed to describe how the wind stress curl in the northeastern South China Sea modulates the circulation southeast of Taiwan on this timescale. The fluctuation with a longer period of 40 ~ 90 days is resulted from the westward propagating eddies.Item 台灣東北海域之模式流場分析(2005) 盧鴻復; Hung-Fu Lu摘要 黑潮是北太平洋最為重要的洋流之一，北赤道流西流碰到陸地後，向北流的一支稱為黑潮，途經菲律賓東岸、呂宋海峽與台灣東部海岸向北方流動，持續輸送具有高溫高鹽特性之熱帶海水至中高緯度地區。當黑潮行至台灣東北部海域時，由於受到呈東西走向之東海陸棚邊緣地形影響，迫使黑潮主軸從向北流動轉變成為向東流動。此處的地形十分複雜，黑潮經台灣東部數千米的水深而來，到達宜蘭外海時先跨越過數百米深之宜蘭海脊，再進入深達兩千米之沖繩海槽南端，之後便遭遇200米高聳之東海陸棚而被迫轉向。過去的觀測發現，在此黑潮轉折處之上層有時會有產生一低溫冷水區域。根據前人的研究，在這個區域裡，冷水團的來源是湧升上至表層的次表層黑潮水，且整層海水都呈現氣旋式的渦漩。表層的反時針冷渦具有季節性的變化，其變化的主要的原因來自於相對應週期的黑潮東西向擺動。 受到冬季海上作業困難的影響，該區域冬季的觀測資料目前所得有限，因此，本研究使用時間與空間四維之數值模式資料來對此海域的流況進行深入之分析與瞭解。我們使用普林斯頓海洋模式（Princeton Ocean Model，POM） 作為基礎，建構了一個範圍在110.5°E到126°E、13.5°N到28°N，空間水平解析度達 1/20° 的北南海數值模式 （Northern South China Sea Model），並利用這個模式來對台灣東北海域小尺度的海洋運動進行模擬。北南海模式運用巢狀箝合的方法，使用大範圍模式 （East Asian Marginal Seas Model） 的模擬結果作為初始與邊界條件，再以北南海模式的模擬結果來分析台灣東北部海域1999-2003年的水文與流場。 北南海模式成功地重建了台灣東北海域的流場與水文狀況。模式模擬的黑潮入侵東海陸棚現象、台灣海峽出口的海流以及東海陸棚上的流場等，都與過去觀測的結果相當一致，本研究也進一步利用模式資料在時空分布上的連續性優點來探討該海域季節內變化的因子。經過檢視與分析模式輸出的結果，發現在冬季某些時間該海域表層仍然有冷渦反時針流場的出現。為了排除季節性變化的影響，利用調和分析的方法進行去除365天的週期變化，再以EOF進行分析表層20公尺的海水溫度後，得到約30天的季節內變化週期，這個變化週期與黑潮東西向擺動的週期相當接近 （也約在30天左右），因此台灣東北冷渦的表層流場除了文獻所提到的季節性變化週期以外，其季節內變化週期應為30天左右，且其季節內流場的變化也應是受黑潮的季內擺動週期所影響。