| Satellite remote sensing data between 2003 and 2014 has been used to made research on SST,chlorophyll,upwelling strength and the effect of wind to upwelling strength in the summertime Zhoushan upwelling area;Moreover,based on a well-known numerical model,Delft3D,the dynamic mechanism about the form of Zhoushan coastal upwelling was further studied and discussed by changing the different sensitive factor in the models,mainly through computing the hydrological elements in Zhoushan sea area in 2014,like currents,temperature,salinity and so on.The observations of satellite remote sensing data have revealed that the strength of summertime upwelling in Zhoushan varied a lot in different years,among which the strength reached peak values in the year of 2005,2009 and 2013,which showed a cycle variation of 4?5 years.The southly wind in summer,especially in July,had a great effect on the change of SST in Zhoushan coastal upwelling,in which upwelling strength had a good linear relationship with meridional wind,whose correlation coefficient was 0.87;In upwelling area,there existed a higher concentration of chlorophyll than non-upwelling area,and chlorophyll showed a negative correlation with SST.The tide results of basic control experiment by Delft3D model agreed well with observation data,the same with SST and salinity,whose root-mean-square errors were within 1? and about 2 ppt.The simulation SST showed a similar distribution and evolution with that of satellite remote sensing data in Zhoushan coastal upwelling area in the summer of 2014.All these correct results showed the model could be used for studying upwelling.What's more,in order to recognize the dynamic mechanism of summertime upwelling in Zhoushan coastal area,four kinds of sensitive experiments,no wind simulation and northly wind simulation,no Yangtze river runoff simulation,no tide simulation and no slope topography simulation were carried out.Under both no wind simulation and northly wind simulation,there still existed cold temperature center and the strength of upwelling was slightly weakened under no wind simulation but was weakened a lot under northly wind simulation,Results under both simulation showed that wind has little effect on the form of summertime Zhoushan coastal upwelling,but influenced the SST change and upwelling strength a lot,which could also be seen in the previous results of remote sensing data.The southly wind could strengthen the upwelling while the northly wind would cause the opposite results;Under no Yangtze river runoff simulation,there was some decrease in the strength of upwelling,which showed that Yangtze river runoff has little effect on the form of Zhoushan coastal upwelling,but has certain influence on its strength;Under no slope topography simulation,Zhoushan coastal upwelling was nearly disappear under the flat topography,which could be seen that the slope topography is of great importance to form Zhoushan coastal upwelling;Under no tide simulation,no upwelling could be found from the temperature and salinity distribution in Zhoushan sea area,so that we could conclude that tide was beneficial to form upwelling.In conclusion,Zhoushan coastal upwelling is formed by a variety of power factor,in which the effect of tide and the topography play a dominate role,while the contribution of wind and Yangtze river runoff is small.Due to water mixing effect caused by tide,under the induction of slope topography,cold water in the bottom sea could climb up along the slope topography to the surface water,then form the upwelling.The contribution of wind to the formation of upwelling is very small,but wind has great influence on the changes of upwelling strength. |
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