A patchlike structure of low-salinity water detached from the Chanjiang ''Diluted Water'' (CDW) is frequently observed in the East China Sea (ECS). In this study, the offshore detachment process of CDW into the ECS is examined using a three-dimensional numerical model. The model results show that low-salinity water is detached from the CDW plume by the intense tide-induced vertical mixing during the spring tide period when the tidal current becomes stronger. During the spring tide, thickness of the bottom mixed layer in the sloping bottom around Changjiang Bank reaches the mean water depth, implying that the stratification is completely destroyed in the entire water column. As a result, the offshore detachment of CDW occurs in the sloping side of the bank where the tidal energy dissipation is strong enough to overcome the buoyancy effect during this period. On the other hand, the surface stratification is retrieved during the neap tide period, because the tidal current becomes substantially weaker than that in the spring tide. Wind forcing over the ECS as well as tidal mixing is a critical factor for the detachment process because the surface wind primarily induces a northeastward CDW transport across the shelf region where tide-induced vertical mixing is strong. Moreover, the wind-enhanced cross-isobath transport of CDW causes a larger offshore low-salinity patch, indicating that the freshwater volume of the low-salinity patch closely depends on the wind magnitude.

[1] Seasonal circulation of the Yellow Sea (YS) in response to wind and tidal forces is examined using a three-dimensional numerical model. Wind forcing affects the wintertime circulation of the YS; on the other hand, the summer southerly monsoon is weak and therefore has little impact on the circulation, on the basis of comparative experiments with and without wind conditions. Results indicate that the Yellow Sea Warm Current (YSWC) along the YS trough exists regardless of wind forcing. However, strong winter northerly winds intensify the southward coastal flows along both coasts of the YS, and therefore, the northward intrusion of the YSWC becomes stronger. These flows in the YS are substantially weakened when wind forcing is not applied to the model. In addition to wind-driven circulation, tide-induced circulation is also dominant in the YS, particularly in summer. In winter, the tidal effect weakens the upwind and downwind flows in response to the strong northerly winds, while in summer, tidal forcing induces a strong southward residual flow along the western slope and a cyclonic gyre with a bottom cold water dome at the central region of the YS. The southward residual current possibly explains the southward movement of the Yellow Sea Bottom Cold Water as observed in summer. Comparison to the effects of parameterized tidal mixing suggests that residual flow driven by explicit tidal forcing plays an important role in the summertime circulation of the YS.

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[1] Altimeter data have significantly improved our understanding of regional sea level variability and trends, but their relatively short records do not allow either evaluation of the ocean state prior to 1993 or multidecadal low-frequency signals in the ocean. Here we characterize and quantify the multidecadal regional sea level rise (rSLR) and related ocean heat content in the Pacific from a non-Boussinesq ocean circulation model in comparison with data sets from altimeters, two sea level reconstructions, and in situ ocean profiles from 1958 to 2008. We show that the rSLR trends have undergone two shifts, during the mid1970s and in the early 1990s, with an east-west dipole pattern in the tropical Pacific. In each of these phases, rSLR accelerated on one side of the Pacific, but decelerated on the other side. The multidecadal sea level shifts can be explained by the dynamical (steric) upperocean responses to the surface wind forcing associated with the Pacific Decadal Oscillation (PDO), with negligible contributions from internal (depth-integrated) ocean mass changes. Additional model experimentation further confirms that the Pacific wind stress trend over the recent two decades has played an important role in strengthening the rSLR in the western Pacific while suppressing the rSLR in the eastern Pacific. The climate-forced large-scale rSLR variability is likely to impose a long-term and uneven impact on coastal communities.