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東南亞河川流域及海洋之碳循環---南海海水通之數值模擬研究值(VI)
No full text[[abstract]]The South China Sea (SCS), bordered by the Asian continent, Borneo, Palawan, Luzon and Taiwan, is the largest marginal sea in the Southeast Asian waters. A string of islands on the east side of the basin separates the sea from the Pacific with three openings. The Luzon Strait is the widest and deepest, allowing inflow and outflow of deep waters. The other two on the northern and southern ends of Palawan exchange waters with the Sulu Sea. The East China Sea to the north and the Java Sea to the south also exchange surface waters with the basin through the Taiwan Strait and the Sunda Shelf, respectively. A small amount of surface water exchanges with the Indian Ocean through the Strait of Malacca. The study of water budget on the SCS is limited because of the complex topographic setting. In the present study, we improve the East Asian Marginal Seas (EAMS) model by adding river runoff and precipitation/evaporation information into the model, bringing the complete model setting for the water budget of the entire basin. The EAMS model domain extends from 99?E to 140?E in longitude, and from 0?N to 42?N in latitude with a horizontal resolution of 1/8? and 26 sigma levels. Since the improved model resolves temporal and spatial scales of interest, we will use the results to discuss the intraseasonal, seasonal and interannual variations of the SCS. Beyond the seasonal time scale, circulation of the SCS demonstrates an interannual variation related to El Ni?o/Southern Oscillation (ENSO). Many recent studies reveal that the ocean dynamics and horizontal advection in particular play a key part in the interannual variability in the SCS. To further highlight the influence from the ocean dynamics on the interannual variability over the SCS, satellite SSH (sea surface height) field instead of SST (sea surface temperature) has been selected for the present study since the oceanic dynamics is better represented by SSH rather than SST, which suffered the heavy influence from the atmosphere (e.g. surface heat flux; evaporation cooling).
Fine-Resolution Modeling Studies in the Northern South China Sea
No full text[[abstract]]Recently, there have been many new observations from expeditions and
moored instruments in the northern South China Sea (NSCS), which
produced several exciting new features not known before. These new
findings call for a new generation of models to explore the processes
responsible for these features, because most of the existing numerical
models can not either resolve them or account for the physics behind
them. A fine-resolution, hydrodynamic model of the NSCS area capable
of resolving the temporal and spatial scales of corresponding oceanic
processes and bringing together the unique oceanographic data sources
available in this area is established in this study. The
fine-resolution NSCS model is nesting to a North Pacific Ocean model.
Description of the circulation is further improved by assimilating the
TOPEX/Poseidon satellite altimeter data into the NSCS model. Data
assimilation model not only reproduces the seasonal patterns in the
earlier studies but also resolves mesoscale highs and lows in the
region. The model results are reasonably consistent with the limited
observations during previous expeditions. The spatial and temporal
variations in the NSCS are discussed as well. Furthermore, satellite
remote sensing data and time series data obtained from moored
instruments (SEATS) will be also used for comparison with model
output.
西北太平洋颱風潛熱(Tropical Cyclone Heat Potential TCHP)之研究
No full text[[abstract]]在近來的研究中有相當多的證據顯示颱風強度的增加與海洋中的暖特徵現象
(warm oceanic features)有關，並且利用颱風潛熱(TCHP)來代替傳統的海水表
面溫度(SST)來研究颱風的強度(Shay 2000, Goni & Trinanes 2003)，因為
SST只能代表的海水表面溫度而無法代表上層海洋的垂直結構(Upper ocean
thermal structure)，因此TCHP能夠清楚地描述海洋的暖特徵，如暖渦(warm
core ring, WCR)；早在1972年Leipper就把TCHP 定義出來，但由於當時沒有衛
星資料的幫助，一直無法運用，直到近年由於衛星遙測的進步，才被開始被應用
，TCHP的定義是從海面到26度C等溫線的垂直溫度積分，如下：Q/sub
H/(x,y,t)=.rho.C/sub p/.int./sup 0//sub (Y=26)) .DELTA.T(x,y,z,t)dz每
年有不少的強烈颱風在西北太平洋(Northwest Pacific Ocean, NWPO)產生出來
，但目前全球對颱風強度的預測並不是很理想，因此藉著研究NWPO的TCHP和
TCHP與颱風之間的關係來提昇我們對颱風強度之預測。本研究是採用美國海軍實
驗室(US Naval Research Laboratory)所發展的三維數值模式(NPACNFS, North
Pacific Ocean Nowcast/Forecast System)，此模式是修改自Princeton Ocean
Model (Blumberg and Mellor, 1987)，使模式能作資料同化(data
assimilation)，其作同化的資料有T/P的SSHA和由衛星所得到的海表面溫度
(SST)。整個太平洋模式蓋了16度S~60度N，99度E~77度W的區域，而模式的垂直
解析度是用26層的sigma-levels組成，在上層海洋的分層數比較密，所以此模式
對上層海洋的解析度比較高，有利於對上層海洋的研究。利用此模式的結果，可
以算出北太平洋的TCHP。本研究並把由NPACNFS 和由美國大氣海洋總署(AOML)利
用來two-layer reduced gravity model 計算出來2003 年夏天的TCHP作比較。
Why are there upwellings on the northern shelf of Taiwan under northeasterly winds?
No full text[[abstract]]Upwellings are observed on the northern shelf of Taiwan during northeasterly winds. Analytical and realistic numerical models are used to explain how vertical motions are created by divergence and convergence produced by wind acting on the vorticity field of two strong jets: the Kuroshio and the Taiwan Warm Current. The seaward increase in cyclonic vorticity near the Kuroshio’s western edge favors a stronger Ekman transport away from the jet, producing upwelling at the shelfbreak under a northeasterly wind. A similar mechanism for generating vertical motions is found across the Taiwan Warm Current. The numerical model results indicate that the vorticity effects can account for up to 30%–50% of the total variation in the surface Ekman transport. Except during summer’s weak southwesterlies, northeasterly wind is dominant over the East China Sea, suggesting that the vorticity effects may be prominent in the observed shelfbreak upwelling in nonsummer months.
Properties of Rossby Waves and Mesoscale Eddies in the South China Sea Derived from Satellite Data and a Numerical Model
No full textVariability analysis of Kuroshio intrusion through Luzon Strait using growing hierarchical self-organizing map
No full text[[abstract]]An advanced artificial neural network classification algorithm is applied to 18 years of gridded mean geostrophic velocity multi-satellite data to study the Kuroshio intrusion into the South China Sea through the Luzon Strait. The results suggest that the Kuroshio intrusion may occur year round. However, intrusion is not the major characteristic of the region. The intrusion mode occurs only 25.8 % of the time. Winter intrusion events are more frequent than summer events. Both stronger intrusion (which is related to wind speed) and weaker intrusion (which may be related to the upstream Kuroshio transport) may occur during winter, but stronger intrusion is dominant. In summer, the Kuroshio intrusion is almost the weaker type. The Kuroshio intrusion through the Luzon Strait usually occurs when the Pacific decadal oscillation index is positive (72.1 % of the time). This study shows that growing hierarchical self-organizing map is a useful tool for analyzing Kuroshio intrusion through the Luzon Strait.
