教師著作

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Subject: search.filters.subject.Luzon Strait

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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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    Blocking and westward passage of eddies in the Luzon Strait.
    (ELSEVIER, 2010-10-01) Sheu, W.-J.; C.-R. Wu; L.-Y. Oey
    Satellite observations have shown the abundance of generally westward-propagating eddies in the subtropical regions in the North Pacific Ocean, especially north of 10衹. Eddies transport mass, and can significantly impact the circulation as well as the heat, salt and nutrient balances of the western Pacific marginal seas. This paper uses a numerical model to examine the conditions when eddies can or cannot freely propagate westward through the Luzon Strait into the South China Sea (SCS). Composite analyses on the 10-year model data show that the fates of eddies depend on the strength and path of the Kuroshio. In one path that exists mostly during fall and winter, the Kuroshio loops westward into the SCS, the potential vorticity (PV) across the current is weak, and eddies are likely to propagate freely through the Luzon Strait. In another path, which exists mostly during spring and summer, the Kuroshio tends to leap directly northward bypassing the SCS, the PV across it strengthens, and eddies are then blocked and are constrained to also follow the northward path. Nonlinear eddy-current interaction and the existence of a cyclone north of the Luzon Island during the looping phase explain why eddies of both signs can pass through the strait. It is shown also that the upstream state of the Kuroshio in the western tropical Pacific plays an important role in dictating the different paths of the Kuroshio. The looping (leaping) path is caused by a weakened (stronger) Kuroshio transport related to the northward (southward) shift of the North Equatorial Current in wintertime (summertime).
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    Mesoscale eddies in the northern South China Sea
    (ELSEVIER, 2007-07-01) Wu, C.-R.; T.-L. Chiang
    A fine-grid resolution model with realistic bathymetry and forcing has been developed to study the characteristics of the mesoscale eddies for the northern South China Sea (SCS). The SCS model derives its open-boundary conditions from a larger-scale model, which minimizes errors related to the uncertainty of the Kuroshio intrusion at the open boundaries. The model results are consistent with previous observations. Model sea-surface height anomaly demonstrates that the hydrography and circulation in the northern SCS are modulated by westward-propagating mesoscale eddies originating in the vicinity of the Luzon Strait. This explains the observed intra-seasonal fluctuations at the SouthEast Asian Time-series Study (SEATS) station. The mesoscale eddies have the same propagation speed as baroclinic Rossby waves (∼0.1 ms−1). The periods of eddy shedding estimated from Strouhal number are around 40–50 days in December and 80–120 days in August, respectively. The seasonal variability of the Kuroshio intrusion results in more eddies in winter than in summer.