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.Y.-C. Hsin

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    The forcing mechanism leading to the Kuroshio intrusion into the South China Sea
    (American Geophysical Union (AGU), 2012-07-01) Wu, C.-R.; Y.-C. Hsin
    We use a high-resolution numerical model to examine the forcing mechanism responsible for Kuroshio intrusion into the South China Sea (SCS). The collective wisdom is that variations in Kuroshio intrusion are closely related to the wind, inside or outside the SCS. A series of experiments was performed to identify the wind-related forcing regulating the intrusion. The experiments demonstrated that the importance of wind inside the SCS is greater than that outside the SCS. Furthermore, the northwestward Ekman drift due to northeasterly wind in winter intensifies the upstream Kuroshio in the Luzon Strait, enhancing the Kuroshio intrusion into the SCS. In particular, the wind stress curl (WSC) off southwest Taiwan is chiefly responsible for the Kuroshio intrusion. Both the WSC and intrusion show both seasonal and intraseasonal variation. As the negative WSC off southwest Taiwan becomes stronger, it contributes to anticyclonic circulation. The enhanced anticyclonic circulation helps the development of the Kuroshio intrusion. The consistency between WSC variability and the intrusion suggests that the WSC off southwest Taiwan is essential to the Kuroshio intrusion variability.
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    Why does the Kuroshio northeast of Taiwan shift shelfward in winter?
    (Springer-Verlag, 2010-04-01) Oey, L.-Y.; Y.-C. Hsin; C.-R. Wu
    Observations indicate that off the northeastern coast of Taiwan a branch of the Kuroshio intrudes farther northward in winter onto the shelf of the East China Sea. We demonstrate that this seasonal shift can be explained solely by winter cooling. Cooling produces downslope flux of dense shelf water that is compensated by shelfward intrusion. Parabathic isopycnals steepen eastward in winter and couple with the cross-shelf topographic slope (the “JEBAR” effect) to balance the enhanced intrusion. The downslope flow also increases vortex stretching and decreases the thickness of the inertial boundary layer, resulting in a Kuroshio that shifts closer to the shelf break.
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    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. Hsin
    The 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.
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    Effects of sea level change on the upstream Kuroshio Current through the Okinawa Trough
    (American Geophysical Union (AGU), 2006-08-01) Kao, S. J.; C.-R. Wu; Y.-C. Hsin; M. Dai
    Sea-level effects on the Kuroshio Current (KC) in the Okinawa Trough (OT) are examined using a 3-D ocean model. When the sea level is −135 m (for the Last Glacial Maximum), topographic high at the southernmost OT partially blocks the KC throughflow, resulting in a 43% reduction of KC inflow. Meanwhile, meandering is enhanced and deepwater ventilation is reduced. However, the KC does not migrate to the east off the OT as suggested previously. When sea level is −40 m (for the beginning of Holocene), the modeled flow pattern resembled present KC in terms of flow path and volume transport. Sea level fluctuation may act as a major control altering the KC course in the OT, leading to significant changes in horizontal and vertical water exchange. It may alter surface water properties, biogeochemistry in both water column and sediments below, potentially, downstream KC and climate over the northeast Asia.
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    Volume transport through the Taiwan Strait : a numerical study.
    (the Chinese Geoscience Union, 2005-06-01) Wu, C.-R.; Y.-C. Hsin
    A fine grid resolution model with realistic bathymetry was constructed to study the spatial and temporal structures of flow through the Taiwan Strait where observations are limited. The model covers an expanded domain that includes the entire East China Sea and South China Sea, as well as the region occupied by the Kuroshio. The fine-resolution model derives its open boundary conditions from a larger scale Western Pacific Ocean model. Two numerical weather products from the European Center for Medium-Range Weather Forecasts and National Centers for Environmental Prediction, and one satellite observation-based wind set (QSCAT) are used to force the ocean model. Model experiments suggested that the best simulation is achieved when the model is driven by the QSCAT wind forcing. Several important features are reproduced in the model simulation. The volume transport is northward and largest in summer while minimal volume transport is southward and occurs in fall and winter. The general trend of volume transport is related to the seasonal reversal of monsoon winds. The present model also suggests that flow in the entire Taiwan Strait is to the southwest during periods of strong northeasterly wind. The annual average transport based on the present model is 1.09 Sv (1 Sv = 10 m s 6 3 1 −), which is smaller than most published values based on shipboard Acoustic Doppler Current Profiler (sb-ADCP) observations. The result suggests that sb-ADCP observations are biased toward estimates in summer and fair weather since bad weather during the winter northeast monsoon often prevents seagoing observations.