Summer Surface Cold Patches In The Yellow Sea: Effects Of Spring-neap And Flood-ebb Variations

Generally the sea surface temperature(SST)attains its maximum in summer.In the Yellow Sea,however,there often exist solitary summertime cold surface patches,called surface cold patches,or SCPs for short.The SCPs make an important hydrographic phenomenon in the East China Sea;they are usually generated in spring,become strongest in summer,and decay in autumn.By observation there are three typical major SCPs,namely,Subei SCP,Shandong SCP,and Mokpo SCP.Previously their generation has been attributed to tidal mixing and tide-induced upwelling.In this study,using the improved ECOM-si model,together with the satellite and in-situ observations,we analyzed the variations of these SCPs during spring-neap and flood-ebb cycles,and found that they actually may not exist all the time in summer,implying that there is still room for improvement for the previously recognized mechanism(s).Specifically,the three major SCPs actually have different evolution patterns over spring-neap cycles.For the Subei SCP,it shows conspicuous spring-neap variations.During neap tide phases,the tidal current is quite weak and hence tide-induced mixing and upwelling are weak.As a result,the surface heat flux dominates the upper layer,strong stratification is then established,as a result,the SCP is suppressed or even disappeared.During spring tide phases,the opposite is true.The strong tidal current,together with the resulting strong tidal mixing and tide-induced upwelling,makes the water column well mixed.The lowest temperature,hence the strongest SCP,occurs during the spring tide days(about two days after a full or new moon).The Mokpo SCP has essentially similar variation patterns.The Shandong SCP,however,doesn't show conspicuous spring-neap variations.This is attributed to the small spring-neap tide current difference.The model results show that spring-neap variation of the Subei and Mokpo SCPs can reach as high as 2? and 3?,respectively,while the Shandong SCP has only a 1? difference.A composite analysis of the multiple years' satellite in-situ buoy observational data further confirms this observation.For this reason,the spring-neap variations should be taken into account,as well as the widely accepted mechanisms,in explaining the formations of the SCPs in the Yellow Sea.In addition to the above,we have also analyzed the SCP evolutions over the flood-ebb cycles,during which the tidal strain effect may make a difference.This is particularly obvious in the Subei SCP;the water column in the SCP area becomes more stratified during ebbing but less stratified during flooding.This effect is pronounced during spring tide phases and is weakened during neap tide phases.In contrast,the Shandong and Mokpo SCPs don't show conspicuous flood-ebb variations,due to the weak vertical current shear in their respective regions.