MASNUM wave-tide-circulation coupled numerical model (MASNUM coupled model, hereinafter) is developed based on the Princeton Ocean Model (POM). Both POM and MASNUM coupled model are applied in the numerical simulation of the upwelling off Yangtze River estuary and in Zhejiang coastal waters in summer. The upwelling mechanisms are analyzed from the viewpoint of tide, and a new mechanism is proposed. The study suggests that the tidally inducing mechanism of the upwelling includes two dynamic aspects: the barotropic and the baroclinic process. On the one hand, the residual currents induced by barotropic tides converge near the seabed, and upwelling is generated to maintain mass conservation. The climbing of the residual currents along the sea bottom slope also contributes to the upwelling. On the other hand, tidal mixing plays a very important role in inducing the upwelling in the baroclinic sea circumstances. Strong tidal mixing leads to conspicuous front in the coastal waters. The considerable horizontal density gradient across the front elicits a secondary circulation clinging to the tidal front, and the upwelling branch appears near the frontal zone. Numerical experiments are designed to determine the importance of tide in inducing the upwelling. The results indicate that tide is a key and dominant inducement of the upwelling. Experiments also show that coupling calculation of the four main tidal constituents (M 2 , S 2 , K 1 , and O 1 ), rather than dealing with the single M 2 constituent, improves the modeling precision of the barotropic tide-induced upwelling.upwelling, dynamic mechanism, numerical simulation, tidal movement, tidal mixing front Large-scale red tides (harmful algal bloom) of thousands of square kilometers occur in the upwelling area off Yangtze River estuary (YRE) and near Zhoushan in recent consecutive years [1] , and these waters have been serious red tide disaster areas in China. Despite the small magnitude, upwelling provides a dynamic background for red tides because it carries nutrients from deep water to the euphotic zone and promotes the growth of planktons. Besides, upwelling is also an important dynamic factor for the formation of fisheries. Therefore the study on the upwelling off YRE and Zhejiang coast is of great ecological and biogeochemical significance.The study area is shown as Figure 1. After its first formal report in 1993 [2] , the summer upwelling off YRE is seldom studied for a long time until recently, when Zhu [3] analyzed the mechanism based on field observation and numerical experiments. Zhu [3] suggested that the causations of the upwelling on the north and south sides of the submarine valley off YRE are baroclinic effects and the baotropic effects related to the intrusion of Taiwan Warm Current (TWC) on continental shelf, respectively, and wind has only very small effect on the upwelling. According to Zhao et al. [4] , the upwelling off YRE is mainly a result of the interaction between TWC
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