[1] The mechanisms of upwelling off the Yangtze River estuary (YRE) and in the adjacent waters in boreal summer are studied using numerical modeling. First, the persistent feature of this phenomenon is confirmed using cruise observations, satellite sea surface temperature (SST), and SST climatologic data. Then, the MASNUM (Marine Science and Numerical Modeling) wave-tide-circulation coupled numerical model is employed to simulate the upwelling patterns. On the basis of the simulation, a set of numerical experiments are designed to explore the main mechanisms inducing the upwelling. The results suggest that tidal mixing plays a predominant role in inducing the upwelling. In offshore waters, strong tidal mixing results in considerable horizontal density gradient across tidal fronts. Upwelling is induced as a branch of the secondary circulation, which is stimulated by the cross-frontal density gradient. Topography also exerts profound influences on upwelling by steering bottom currents to ascend upward and regulating tidal fronts in both location and intensity. Besides the tides and topography, other dynamical factors also alter the strength of upwelling locally. The Yangtze River discharge (YRD) and Taiwan Warm Current (TWC) account partly for the upwelling off the YRE and near Zhoushan Islands, respectively. The influence of wind on upwelling is small. In the coastal waters near Zhoushan Islands, the wind forcing exerts negative influences on upwelling by weakening the encroachment of TWC onto the continental shelf, which may exceed the positive effects of Ekman pumping.

A theoretical framework to include the influences of nonbreaking surface waves in ocean general circulation models is established based on Reynolds stresses and fluxes terms derived from surface wave-induced fluctuation. An expression for the wave-induced viscosity and diffusivity as a function of the wave number spectrum is derived for infinite and finite water depths; this derivation allows the coupling of ocean circulation models with a wave number spectrum numerical model. In the case of monochromatic surface wave, the wave-induced viscosity and diffusivity are functions of the Stokes drift. The influence of the waveinduced mixing scheme on global ocean circulation models was tested with the Princeton Ocean Model, indicating significant improvement in upper ocean thermal structure and mixed layer depth compared with mixing obtained by the Mellor-Yamada scheme without the wave influence. For example, the model-observation correlation coefficient of the upper 100-m temperature along 35°N increases from 0.68 without wave influence to 0.93 with wave influence. The wave-induced Reynolds stress can reach up to about 5% of the wind stress in high latitudes, and drive 2-3 Sv transport in the global ocean in the form of mesoscale eddies with diameter of 500-1,000 km. The surface waveinduced mixing is more pronounced in middle and high latitudes during the summer in the Northern Hemisphere and in middle latitudes in the Southern Hemisphere.

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[1] The dynamic mechanisms of the upwelling off the East China Sea (ECS) coast in wintertime are studied. First, the upwelling signals off the ECS coast are identified by the observed temperature, salinity, nutrients, and dissolved oxygen data obtained during the cruises in January 1999. The MASNUM wave-tide-circulation coupled model is then employed to simulate the hydrography of the ECS. Comparisons between the simulations and observations show that the model performance is satisfactory. On the basis of successful simulation, four numerical experiments are conducted to investigate the upwelling mechanisms. The results suggest that the density (or salinity) front, which separates the inshore Low Salinity Coastal Water and the offshore Taiwan Warm Current (TWC), is the primary inducement for the upwelling. Owing to strong density gradient, the baroclinic pressure gradient force (PGF) is quite large near the frontal zone, and this PGF elicits an upwelling branch along the topography slope. Wind, TWC, and tide affect the density front in extension and intensity, thus exerting subsidiary influences on the upwelling. According to Ekman's theory, the northerly monsoon is downwelling favorable. However, the net effects of wind on the upwelling off the ECS coast in winter are positive because it drives the Changjiang River Diluted Water (CDW) flowing southward and forms the density front. Similarly, the resultant effects of TWC on the upwelling are negative for obstructing the pathway of CDW. Tide contributes to the upwelling because tidal mixing facilitates the expansion of CDW.

The summertime upwelling off the west coast of Hainan Island is newly detected by satellite remote sensing sea surface temperature, and confirmed by both historical field observations and numerical modeling. Furthermore, numerical experiments are conducted to gain understanding of the upwelling mechanisms. A tidal mixing front (TMF) is identified as the vital factor triggering the formation of the upwelling. The baroclinic pressure gradient force, which stems from the intense density difference across the TMF, causes a frontal‐scale circulation at the TMF. As a result, upwelling appears as a branch of this circulation. The southwest monsoon induces downwelling, which competes with the front‐induced upwelling. Climatologically, the upwelling dominates and can reach about 5 m below the sea surface above the slope bottom. In calm weather with no or weak winds, it is expected that the upwelling can reach all the way to the sea surface.