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Effects of tidal currents on winter wind waves in the Qiongzhou Strait: a numerical study
Peng Bai, Zheng Ling, Cong Liu, Junshan Wu, Lingling Xie
2020, 39(11): 33-43. doi: 10.1007/s13131-020-1673-2  Published:2020-11-25
Keywords: Qiongzhou Strait, COAWST, significant wave height, peak wave direction
Effects of currents on winter wind waves in the tide-dominated Qiongzhou Strait (QS) were numerically evaluated via employing the coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system. Validations showed satisfactory model performance in simulating the intense tidal currents in the QS. Different effects of sea level variations and tidal currents on waves were examined under the maximum eastward (METC) and westward (MWTC) tidal currents. In the east entrance area of the QS, the positive sea levels under the MWTC deepened the water depth felt by waves, benefiting the further propagation of wave energy into the inner strait and causing increased wave height. The METC and the MWTC could both enhance the wave height in the east entrance area of the QS, mainly through current-induced convergence and wavenumber shift, respectively. By current-induced refraction, the METC (MWTC) triggered counterclockwise (clockwise) rotation in peak wave directions in the northern part of the QS while clockwise (counterclockwise) rotation in the southern part.
Effects of wave-current interaction on the waves, cold-water mass and transport of diluted water in the Beibu Gulf
Jingling Yang, Shaocai Jiang, Junshan Wu, Lingling Xie, Shuwen Zhang, Peng Bai
2020, 39(1): 25-40. doi: 10.1007/s13131-019-1529-9  Published:2020-01-20
Keywords: wave-current interaction, Beibu Gulf, river plume, cold-water mass, COAWST
Wave-current interaction and its effects on the hydrodynamic environment in the Beibu Gulf (BG) have been investigated via employing the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) modeling system. The model could simulate reasonable hydrodynamics in the BG when validated by various observations. Vigorous tidal currents refract the waves efficiently and make the seas off the west coast of Hainan Island be the hot spot where currents modulate the significant wave height dramatically. During summer, wave-enhanced bottom stress could weaken the near-shore component of the gulf-scale cyclonic-circulation in the BG remarkably, inducing two major corresponding adjustments: Model results reveal that the deep-layer cold water from the southern BG makes critical contribution to maintaining the cold-water mass in the northern BG Basin. However, the weakened background circulation leads to less cold water transported from the southern gulf to the northern gulf, which finally triggers a 0.2°C warming in the cold-water mass area; In the top areas of the BG, the suppressed background circulation reduces the transport of the diluted water to the central gulf. Therefore, more freshwater could be trapped locally, which then triggers lower sea surface salinity (SSS) in the near-field and higher SSS in the far-field.
Upwelling off the west coast of Hainan Island: sensitivity to wave-mixing
Bai Peng, Yang Jingling, Zhang Shuwen, Xie Lingling, Wu Junshan
2019, 38(11): 11-19. doi: 10.1007/s13131-019-1494-3
Keywords: upwelling|wave-mixing|tidal mixing front|COAWST|Hainan Island, , , ,
The coupled ocean–atmosphere–wave–sediment transport (COAWST) modeling system is employed to investigate the role of wave-mixing playing in the upwelling off the west coast of Hainan Island (WHU). Waves, tides and sea surface temperature (SST) are reproduced reasonably well by the model when validated by observations. Model results suggest the WHU is tidally driven. Further investigations indicate that inclusion of wave-mixing promotes the intensity of the WHU, making the simulated SST become more consistent with remote-sensed ones. Dynamically, wave-mixing facilitates the “outcrop” of more upwelled cold water, triggering stronger WHU and leading to a three-dimensional dynamical adjustment. From the perspective of time, wave-mixing contributes to establishing an earlier tidal mixing front strong enough to generate WHU and that is, WHU may occur earlier when taking wave-mixing into consideration.
Development of a fine-resolution atmosphere-wave-ocean coupled forecasting model for the South China Sea and its adjacent seas
Sun Junchuan, Wei Zexun, Xu Tengfei, Sun Meng, Liu Kun, Yang Yongzeng, Chen Li, Zhao Hong, Yin Xunqiang, Feng Weizhong, Zhang Zhiyuan, Wang Yonggang
2019, 38(4): 154-166. doi: 10.1007/s13131-019-1419-1
Keywords: South China Sea, COAWST model, MASNUM model, atmosphere-wave-ocean forecasting system, data assimilation
A 72-h fine-resolution atmosphere-wave-ocean coupled forecasting system was developed for the South China Sea and its adjacent seas. The forecasting model domain covers from from 15°S to 45°N in latitude and 99°E to 135°E in longitude including the Bohai Sea, the Yellow Sea, the East China Sea, the South China Sea and the Indonesian seas. To get precise initial conditions for the coupled forecasting model, the forecasting system conducts a 24-h hindcast simulation with data assimilation before forecasting. The Ensemble Adjustment Kalman Filter (EAKF) data assimilation method was adopted for the wave model MASNUM with assimilating Jason-2 significant wave height (SWH) data. The EAKF data assimilation method was also introduced to the ROMS model with assimilating sea surface temperature (SST), mean absolute dynamic topography (MADT) and Argo profiles data. To improve simulation of the structure of temperature and salinity, the vertical mixing scheme of the ocean model was improved by considering the surface wave induced vertical mixing and internal wave induced vertical mixing. The wave and current models were integrated from January 2014 to October 2015 driven by the ECMWF reanalysis 6 hourly mean dataset with data assimilation. Then the coupled atmosphere-wave-ocean forecasting system was carried out 14 months operational running since November 2015. The forecasting outputs include atmospheric forecast products, wave forecast products and ocean forecast products. A series of observation data are used to evaluate the coupled forecasting results, including the wind, SHW, ocean temperature and velocity. The forecasting results are in good agreement with observation data. The prediction practice for more than one year indicates that the coupled forecasting system performs stably and predict relatively accurate, which can support the shipping safety, the fisheries and the oil exploitation.