The Study On Yellow Sea Warm Current’s Mechanism And Sea Level Low-frequency Fluctuations In Bohai And Yellow Sea During Winter Storm

With the analysis of mooring ADCP current data in Northern Yellow Sea,barotropic current oscillation in lower frequency than that of tides coupled withresidual sea level fluctuations during winter time is discussed in this study incombination with a three-dimensional numerical model developed by ROMS. Thesimulated results from extensive tests indicate that the sea level low-frequencyfluctuation is not accidental, but a common phenomenon occurs in winter. Theextreme influence region of this fluctuation can reach31oN. Compare with the seasurface air press and heat flux, the meridional sea surface wind stress is the mainreason which caused the low-frequency sea level fluctuation in Bohai Sea and YellowSea. The influence of local wind (north of29oN，west of130oE) is a requirement forsea level low-frequency fluctuation. The impact of the local wind is small in BohaiSea and North Yellow Sea considering the wind fetch. The main reason for drawdownis the pumping effect caused by the wind stress of South Yellow Sea. The decreasedwater of South Yellow Sea is principally controlled by local wind. The wind stressupon the East Sea region, which next to the Yellow Sea, also makes effort to thedrawdown of Bohai and Yellow Sea.Steady wind can’t inspire sea levelfluctuations.Thus, time-varying meridional wind stress is extremely important.The combined action of wind-driven sea level slope and kelvin wave after windweakened is considered to the mechanism of sea level fluctuation. During the growingprocess of wind stress, the sea level slope is dominant. When the north windweakened, sea level variation is controlled by the kelvin wave that propagatessouthward (northward) along the west (east) boundary. The zonal variation of waterdepth only affects the amplitude of the sea level fluctuation.The essential mechanism of the current oscillation is the interaction of thewind-driven current and the southward (northward) propagated Kelvin wave along thewest (east) which mentioned above. So the sea level fluctuation and currentoscillation are controlled by the same mechanism. It indicates that the coupling of sealevel fluctuation and current oscillation is inevitable. As the different patterns of onemechanism, they have similar extreme influence range. The sea level low-frequencyfluctuation can be considered as the evidence of current oscillation, which provides agood access to the research of the winter circulation system in the Bohai Sea and theYellow Sea.The Yellow Sea Warm Current is not an intermittent compensated flow caused bythe weaken north wind, but a stable flow with two features of stable state andbarotropic state. It exhibits the stable state when wind is weak, while appears thebarotropic state with strengthened velocity under the strong wind process. With the analysis of ideal model, the current oscillation is advantageous to the southwardmovement of the high-latitude boundary area water body as well as the northwardshift of the low-latitude central area.With the research of water mass transport across the Bohai Strait during thecurrent oscillating, the drawdown of Bohai Sea was mainly casued by the loss ofwater. The salt transport indicates that the Yellow Sea water flows into the Bohai Sea.In other word, the current oscillation contributes to a significant influence on waterexchange of Bohai Sea. This paper innovatively proposes a research method toanalyze annual salinity change of the Bohai Sea through water exchange. Besides,based on the conclusion referred to above that the sea level low-frequency fluctuationcan be the evidence of the current oscillation，an inference that the winter sea levellow-frequency fluctuation is the very important factor effect the salinity change of theBohai Sea drawn by this paper.