教師著作

Permanent URI for this collectionhttp://rportal.lib.ntnu.edu.tw/handle/20.500.12235/37078

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Author: search.filters.author.S.-Y. ChaoHas files: No

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    An updated examination of the Luzon Strait transport.
    (American Geophysical Union (AGU), 2012-03-01) Hsin, Y.-C.; C.-R. Wu; S.-Y. Chao
    Despite numerous previous estimates of Luzon Strait transport (LST), we attempt an update using a fine-resolution model. With these improvements, the circulation in and around Luzon Strait shows up rather realistically. Intrusion of a Kuroshio meander into the South China Sea (SCS) is seasonally varying. The LST, especially in the upper ocean, caused by a small difference between the large meander inflow and outflow, is also seasonally varying and subject to large standard deviation. The annual mean LST is estimated to be westward (−4.0 ± 5.1 Sv) along 120.75°E. We have also conducted process of elimination experiments to assess the relative importance of open ocean inflow/outflow, wind stress, and surface heat flux in regulating LST and its seasonality. The East Asian monsoon winds stand out as the predominant forcing. Without it, the upper ocean LST changes from westward to eastward (ranging up to 4 Sv) and, with misaligned seasonality, triggering an inflow from the Mindoro Strait to the SCS to replenish the water mass loss. Discounting monsoon winds, sea level in the Sulu Sea is generally higher because it receives the Indonesian Throughflow before the SCS, which causes an inflow from the Sulu Sea to the SCS. On the other hand, the annual mean wind from the northeast invites outflow from the SCS to the Sulu Sea (or inflow from the Luzon Strait). Weighing the two competing factors together, we see the cessation of northeast monsoon as a condition favorable for the Luzon Strait outflow or the Mindoro Strait inflow.
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    Transient, seasonal and interannual variability of the Taiwan Strait Current.
    (Springer Netherlands, 2007-10-01) Wu, C.-R.; S.-Y. Chao; C. Hsu
    We have constructed a fine-resolution model with realistic bathymetry to study the spatial and temporal variations of circulation in the Taiwan Strait (TS). The TS model with a resolution of 3∼10 km derives its open boundary conditions from a larger-scale model. The QSCAT/NCEP winds and AVHRR SST provide forcing at the sea surface. Because of the high resolution in model grids and forcing, the model achieves a previously unavailable level of agreement with most observations. On biweekly time scales surface-trapped current reversals often lead to Strait transport reversals if the northeasterly wind bursts in winter are sufficiently strong. On seasonal time scales the northward current is the strongest in summer since both summer monsoon and pressure gradient force are northward. The summer northward current appears to be relatively unimpeded by the Changyun Rise (CYR) and bifurcates slightly near the surface. With the arrival of the northeast monsoon in fall, downwind movement of China Coastal Water (CCW) is blocked by the northward current near 25.5°N and 120°E. In winter, the northward current weakens even more as the northeasterly monsoon strengthens. The CCW moves downwind along the western boundary; the CYR blocks part of the CCW and forces a U-shaped flow pattern in the northern Strait. Past studies have failed to reveal an anticyclonic eddy that develops on the northern flank of CYR in winter. On interannual time scales a weakened northeast monsoon during El Niño reduces advection of the cold CCW from the north and enhances intrusion of warm water from the south, resulting in warming in the TS.
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    Physical and geographical origins of the South China Sea Warm Current
    (American Geophysical Union (AGU), 2008-08-01) Chiang T.-L.; C.-R. Wu; S.-Y. Chao
    We examine the formation mechanism of the South China Sea Warm Current in winter, using a high-resolution, numerical model. The current, noted for its ability to flow against the prevailing northeast monsoon in winter, has received considerable attentions in recent years. The collective wisdom from previous models points to two likely generation scenarios: occasional wind relaxation or the Kuroshio intrusion. The present model consistently points to the wind relaxation as the dominant mechanism. When comparing differences between previous models and ours, we also conclude that the Kuroshio intrusion helps, but is not chiefly responsible. Tracing the current to the source, we identify the elevated sea level in the Gulf of Tonkin, induced by the northeast monsoon, as the ultimate driving force. The presence of Hainan Island bears little importance in generating the current.
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    A numerical study on the formation of upwelling off northeast Taiwan
    (American Geophysical Union (AGU), 2008-08-01) Wu, C.-R.; H.-F. Lu; S.-Y. Chao
    We examined the spatial and temporal variations of upwelling off northeast Taiwan, using a fine-resolution numerical model with realistic bathymetry. The zonally running shelf break in the area deflects the Kuroshio seaward and produces upwelling on its on-shelf edge. The upwelling, in turn, manifests a cold dome or a cyclonic eddy. In depths below 150 m or so, the upwelling and hence the cyclonic eddy exist year-round. Above this depth, the eddy waxes and wanes as the upper portion of the Kuroshio migrates seaward and shoreward, respectively. The eddy event fluctuates in a wide range of timescales. Seasonally, the occurrence heavily favors summer rather than winter, because the mean Kuroshio axis migrates seaward in summer. Intraseasonally, the fluctuation contains two dominant periods centered at 70 days and 30 days. Local wind forcing and channeling by two local canyons do not affect the eddy statistics significantly.