| Wind plays an important role in modulating coastal hydrodynamic condition and ecosystem.Assessing the trend of sea surface wind is important for understanding the response of the marine environment to the climate change.Analysis of wind data reveals that the summer wind direction in the Pearl River Estuary（PRE）shifts anticlockwise at a rate of -0.34°yr-5over the past 42 years（1979～2020）.With this rate,the mean wind direction shifts from 183.6°（in 1979）to 169.3°（in 2020）.The linearly predicted summertime wind direction will be shifted to 142.1°by 2100.The summer wind speed decreased from 5.02 m?s-1in 1979 to 4.01 m?s-1in 2020,and is predicted as 2.01 m?s-1in 2100.How this long-term change of wind direction and wind speed affects the hydrodynamic structure in the PRE have not been examined.A fully calibrated high resolution 3D hydrodynamic model is used to evaluate the response of local hydrodynamics to wind direction shifting.Analyses indicate that:（1）When the wind direction changes,both the cross-channel Ekman transport and along-channel seaward flow is weakened as wind direction shifting.The resulted lateral circulation is slowed down significantly while the longitudinal exchange flow is weakened slightly.Remarkable increase of stratification occurs in the coastal sea adjacent to the Modaomen where hypoxia has been reported frequently.The residence time of Lingding Bay increased slightly.Momentum budget indicates that major change in transverse direction is the barotropic pressure term,which is mainly balanced by the baroclinic pressure term and diffusion term.However,in the longitudinal direction,the baroclinic and barotropic pressure terms show different trends in the western shoal from the rest,and there is no typical term balance.（2）With the weakening of wind speed,the transverse Ekman transport weakens,while the longitudinal exchange flow strengthens in the surface layer,weakens in the middle layer and strengthens in the bottom layer.In the coastal sea adjacent to the Modaomen,the stratification intensity increases,while the area of hypoxia doesn’t change.The momentum budget indicates in the longitudinal direction the barotropic pressure term decreases significantly,while the diffusion term increases significantly.The change of the barotropic pressure term is mainly balanced by the change of diffusion term.However,there is no typical term balance phenomenon in transverse direction.（3）EOF analysis shows that the variation of current speed and salinity in the channel is mainly dominated by the change of wind speed;the variation of current speed in transverse section is controlled by both the change of wind direction and speed.The first order mode of salinity in transverse section is dominated by wind speed change,and the second mode is controlled by wind direction change. |
