A Comparison Analysis Of The Response Of The Qiongdong Upwelling And The Vietnam Coastal Upwelling To Super El Ni(?)o Events

The Qiongdong Upwelling(QDU)and the Vietnam Coastal Upwelling(VCU)are two of the most prominent summer upwelling in the South China Sea(SCS).The upwelling brings the nutrient-rich cool water up to the surface,enriches local chlorophyll and enhances the primary productivity,so that are important for local fishery and climate.After super El Ni?o events,the QDU and VCU have different response with local environment changing in different ways.In order to reveal the mechanism,we use Sea Surface Temperature(SST),Sea Surface Height(SSH),wind data,and radiation flux data to analyze the different response of the QDU and the VCU after the end of two super El Ni?o events in 1998 and 2016.The results show that in summer 1998,the upwelling-favorite wind anomaly promoted the QDU,while the upwelling-not-favorite wind anomaly hindered the development of the VCU.This is similarly to that of previous studies.As a result,the SST became cooler and covers more area in the QUD region,but warmer and smaller near the Vietnam coast.In the other hand,in summer 2016,cool water shrinks and SST is extremely warmer in the QDU region,though upwelling-favorite wind were stronger.In the VCU region,cool water dose not change cooler either,but even slightly warmer when local wind anomaly being upwelling-favorite.The variation of the upwelling SST is not consistent with that of the wind.Thus,there must be other factors stunting the upwelling to cool the surface water.To find out the dynamic factor blocking the surface cooling of the upwelling,we consider firstly the contribution of the heat flux absorbed by the sea surface.Comparison of the net downward heat fluxes over the QDU and the VCU in summer2016 to that in summer 1998,the results show that the fluxes in 2016 are larger than that in 1998 in both regions,and the increment of heat flux in VCU is near twice larger than that in the QDU.However,the SST decreases with magnitude of 0.98?in the VCU and increases 0.71? in the QDU region.The SST decreased even thoughmore heat absorbed.It could infer that the heat flux is not the dominant factor for the variation of the upwelling.Other factor influencing the SST of the upwelling needs to be revealed,Considering the effects of the oceanic processes,we further analyze the relationship between the variability of the SSH and that of the SST.Comparing the Sea Surface Temperature Anomaly(SSTA)to the Sea Surface Height Anomaly(SSHA),alongshore wind stress anomaly(AWSA),wind speed anomaly(WSPA),and wind stress curl anomaly(WCA)in the upwelling regions,we found that variability of the SSTA is consistent with that of SSHA in the same region during the same period.For a certain region,the increment of AWSA and WCA is the dynamic factor cooling down the SST.For a certain period,the impact of the WCA on the SSTA is larger in QDU than that in the VCU,while the influence of the SSHA and the AWSA to the SSTA in the VCU is stronger than that in the QUD.This is consistent with the existent of the summer strong eddy dipole east off the Vietnam coast.In summary,this study reveals that the eddies indicated by the SSHA,and the wind anomaly,specially the AWSA and the WCA,are two dominant factors controlling the strength of coastal upwelling after super El Ni?o.