教師著作
Permanent URI for this collectionhttp://rportal.lib.ntnu.edu.tw/handle/20.500.12235/37078
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Item 北台灣海峽數值模擬研究(2007-11-30) 張育綾; 吳朝榮; 李忠潘本研究利用一個高解析度的台灣海峽數值模式，根據其海溫、海水流速流向、風向風速等，分析台灣海峽的海水流況，並利用數值模式時間及空間連續的特點，了解台灣海峽流況之年際與季節變化，並根據年際及季節變化中呈現的的特殊暖水現象做進一步的分析及研究。台灣西北海域在春季出現的暖水區域具有年際變化，而暖水的成因為東來的黑潮水與台灣海峽水輻合所致，1999 與2000 年春季為反聖嬰年，輻合較強，故有局部暖水出現，而2001、2002、2003年春季為正常年，輻合較弱，故沒有局部暖水出現。另外分析模式資料也發現台灣東北海域之冷渦現象亦具有年際變化，並且在北台灣海峽與暖水區域形成有趣的一暖一冷現象。Item 臺灣東北海域湧升流之時空變化(2007-11-30) 盧鴻復; 吳朝榮; 李忠潘黑潮為世界重要洋流之一。前人觀測發現黑潮流經臺灣東北海域之時，受到東海陸棚走向之影響，黑潮與複雜的海底地形交互作用，在此處產生湧升流與冷渦現象。過去的研究多以現場觀測為主，難以連貫研究資料的時空變化。因此，本研究以普林斯頓大學所開發之三維海洋數值模式為基礎，採用真實地形與巢狀箝合方法，將較大範圍模式之輸出作為本模式之初始與邊界條件，建構一個水平空間解析度達1/20°之海流模式。本模式可用來模擬臺灣東北海域之海流運動，其結果成功地重建該處之流場與水文型態，藉由分析、研究模式資料，可以瞭解東北海域之流場時空變化。模擬結果顯示，黑潮衝擊陸棚產生湧升流，於表層以冷渦流場表現，此現象受到黑潮運動影響，有季節性的變化，與過去觀測結果一致。除此之外，模式資料更進一步明確表現東北海域冷渦流場在季節尺度內的變化，其資料分析結果反應觀測資料之缺憾，亦指出上層黑潮主軸之擺動週期受到不同機制的作用而有所差異，進而對東北海域之上層流場產生顯著影響。Item Seasonal to interannual variations in the intensity and central position of the surface Kuroshio east of Taiwan(American Geophysical Union (AGU), 2013-09-01) Hsin Y.-C.; B. Qiu; T.-L. Chiang; C.-R. WuSeasonal and interannual changes of surface Kuroshio intensity and central position east of Taiwan during 1993–2012 are investigated by quantitatively analyzing the satellite altimetry product. The Kuroshio moves inshore (offshore) off northeast of Taiwan in winter (summer), whereas it has an offshore (inshore) path off southeast of Taiwan in winter (summer). The seasonal change of heat flux over the East China Sea shelf is found to cause the seasonality of the Kuroshio central position off northeast of Taiwan, whereas the seasonal Kuroshio movement off southeast of Taiwan is found to be induced by the combined effect of the Kuroshio changes through the Luzon Strait and the eastern Luzon Island. In contrast to this y-dependent path changes, the Kuroshio becomes weaker (stronger) as a whole east of Taiwan in winter (summer). On the interannual time scales, the Kuroshio throughout the eastern coast of Taiwan intensifies and has a concurrent offshore path during the periods of 1995–1997 and 2004–2007. The relative intensity of cyclonic eddies to anticyclonic eddies off eastern Taiwan are found to contribute to these interannual Kuroshio changes.Item Fluctuations of the thermal fronts off northeast Taiwan.(American Geophysical Union (AGU), 2011-10-01) Hsin, Y.-C.; T.-L. Chiang; C.-R. WuA high-resolution sea surface temperature (SST) data derived from several satellites is used to investigate the variability of the thermal front off northeastern Taiwan. Hidden by a dominant annual cycle, the SST data cannot reveal the thermal front fluctuation in the form of Hovm闤ler diagram. An innovative methodology has been applied to the SST satellite imagery to derive the SST Standardized Index (SSTSI), capable of revealing the frontal variability with multiple time scales. Principal component analysis shows that the SSTSI variation consists mainly of two modes. Mode 1 represents a strong annual cycle related to the seasonal reversal of the monsoonal winds. The temperature gradient is enhanced in winter and a cold dome is observed off northern Taiwan in summer. Mode 2 is highly correlated with the upstream Kuroshio variability. The shoreward (seaward) migration of the thermal front takes place when the Kuroshio transport weakens (strengthens). The results are consistent with transports estimated by tidal gauge measurements, satellite altimeter-based sea level anomaly, and surface flow patterns derived from high-frequency radars. Mode 2 is coherent with the Kuroshio transport through the East Taiwan Channel at periods of 120 and 45 d with a time lag of 40 and 11 d, respectively. This 120 d fluctuation is due to the interaction between westward-propagating eddies and the Kuroshio east of Taiwan, while the 45 d signal arises from the Kuroshio's self-instability. The interannual variations of the SST pattern in winter and summer are also discussed.Item Air-sea interaction between Tropical Cyclone Nari and Kuroshio(American Geophysical Union (AGU), 2008-06-01) Wu, C.-R.; Y.-L. Chang; L.-Y. Oey; C.-W.J. Chang; Y.-C. HsinThe air-sea interaction between tropical cyclone Nari (Sep/6 – 16/2001) and Kuroshio is studied using satellite observations and an ocean model. Nari crossed the Kuroshio several times, which caused variations in typhoon intensity. Nari weakened when it was over the shelf north of Kuroshio where cooling took place due to mixing of the shallow thermocline. The cyclonic circulation penetrated much deeper for the slowly-moving storm, regardless of Nari’s intensity. Near-inertial oscillations are simulated by the model in terms of the vertical displacement of isotherms. The SST cooling caused by upwelling and vertical mixing is effective in cooling the upper ocean several days after the storm had passed. At certain locations, surface chlorophyll-a concentration increases significantly after Nari’s departure. Upwelling and mixing bring nutrient-rich subsurface water to the sea surface, causing enhancement of phytoplankton bloom.Item Bimodal Behavior of the Seasonal Upwelling off the northeastern coast of Taiwan(American Geophysical Union (AGU), 2009-03-01) Chang Y.-L.; C.-R. Wu; L.-Y. OeyObservations over the outer shelf and shelf break off the northeastern coast of Taiwan indicate a curious seasonal variability of upwelling. At deeper levels 100 m below the surface, upwelling is most intense in summer but weaker in winter. Nearer the surface at approximately 30 m below the surface, the opposite is true and the upwelling is stronger in winter than in summer. Results from a high-resolution numerical model together with observations and simple Ekman models are used to explain the phenomenon. It is shown that the upwelling at deeper levels (∼100 m) is primarily induced by offshore (summer) and onshore (winter) migrations of the Kuroshio, while monsoonal change in the wind stress curl, positive in winter and negative in summer, is responsible for the reversal in the seasonal variation of the upwelling near the surface (∼30 m). This mechanism reconciles previous upwelling data.Item Spatial and Temporal Variations of the Kuroshio East of Taiwan, 1982-2005: A numerical study(American Geophysical Union (AGU), 2008-04-01) Hsin, Y.-C.; C.-R. Wu; P.-T. ShawA 1/8 East Asian Marginal Seas model nested to a larger-domain North Pacific Ocean model is implemented over a span of 24 years from 1982 to 2005 to investigate the spatial and temporal variations of the Kuroshio east of Taiwan. 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 may branch 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 123–123.5 E between 22 and 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.