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  • Author or Editor: Yang Gao x
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Daosheng Wang, Jicai Zhang, Ya Ping Wang, Xianqing Lv, Yang Yang, Daidu Fan, and Shu Gao

Abstract

The model parameters in the suspended cohesive sediment transport model are quite important for the accurate simulation of suspended sediment concentrations (SSCs). Based on a three-dimensional cohesive sediment transport model and its adjoint model, the in situ observed SSCs at four stations are assimilated to simulate the SSCs and to estimate the parameters in Hangzhou Bay in China. Numerical experimental results show that the adjoint method can efficiently improve the simulation results, which can benefit the prediction of SSCs. The time series of the modeled SSCs present a clear semidiurnal variation, in which the maximal SSCs occur during the flood tide and near the high water level due to the large current speeds. Sensitivity experiments prove that the estimated results of the settling velocity and resuspension rate, especially the temporal variations, are robust to the model settings. The temporal variations of the estimated settling velocity are negatively correlated with the tidal elevation. The main reason is that the mean size of the suspended sediments can be reduced during the flood tide, which consequently decreases the settling velocity according to Stokes’s law, and it is opposite in the ebb tide. The temporal variations of the estimated resuspension rate and the current speeds have a significantly positive correlation, which accords with the dynamics of the resuspension rate. The temporal variations of the settling velocity and resuspension rate are reasonable from the viewpoint of physics, indicating the adjoint method can be an effective tool for estimating the parameters in the sediment transport models.

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Xingru Feng, Junchuan Sun, Dezhou Yang, Baoshu Yin, Guandong Gao, and Weiqi Wan

Abstract

Reasonable parameterization of air-sea momentum flux is important for the accuracy of ocean and atmosphere simulations, and in the numerical model, the parameterization of the air-sea momentum flux becomes a problem of parameterization of the sea surface wind stress drag coefficient (Cd). In this study, five kinds of typical Cd parameterization methods were assessed in the simulation of two typhoon cases, one of which was a super typhoon and another was a common severe typhoon, based on an atmosphere-wave-ocean coupled model. Based on the two case study, it was found that the typhoon path and minimum sea level pressure were not very sensitive to Cd parameterizations, though the spatial distribution of Cd and its variation with wind speed were all very different across the parameterization methods. However, Cd has a significant effect on the wind speed, and at high wind speed, the simulated maximum wind speed compared better with the observation in the experiment which adopted the Cd calculation method considering the effects of sea spray. Also, Cd plays an important role in the feedback processes between atmosphere and ocean during the typhoon process, through its effect on the air-sea heat and momentum flux, SST, ocean mixed layer depth, ocean currents etc. The results of this study answered the question of how the Cd affects the atmosphere and ocean during the typhoon process, and to what extent they are affected, which can help to explain or even further improve the simulation results.

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