Numerical Simulation Of The Change In The Yellow Sea Warm Current

The Yellow Sea Warm Current (YSWC) is a compensational current formed in the center of the Yellow Sea under the forcing of winter monsoon. It has important implications for the environment and ecosystem of the Yellow Sea and the climate in this region. The east Asian winter monsoon has weakened significantly since1950s, and the weakening may cause change in the YSWC on a multi-decadal time scale and thus further affect the regional climate.Two typical periods are selected to analyze the surface wind over the Yellow Sea in winter during1951to2000:a positive phase is defined as1951-1970and a negative phase is defined as1981-2000. Results show that the surface wind over the Yellow Sea has been gradually weakening during1951～2000. In the southern Yellow Sea the wind shows a southwestly anomaly, while in the northern Yellow Sea there is a southerly anomaly.A two-dimensional barotropical numerical model is used to simulate the change in winter circulation in the Yellow Sea during1951～2000. Comparison of the circulations between the positive phase and the negative phase shows that the YSWC and coastal currents have changed significantly:(1) the YSWC and the coastal current both show a trend of weakening during1951～2000, and (2) the weakening of currents forms a anomalous basin-wide anti-cyclonic gyre in the central and western Yellow Sea while generates a relative weak anomalous cyclonic gyre in the eastern Yellow Sea. Further analysis shows that the pattern of the anomalous circulation coincides with that of vorticity of depth-averaged anomalous wind stresses of the winter monsoon, suggesting that the change in winter monsoon is the major forcing for the change of the YSWC.Our numerical results are further verified by observational datasets indirectly. The weakening of surface temperature front is found from two in situ observations along35°N and36°N sections, and one from the data collected by satellite as well. All of these agree very well with the change in circulations simulated by the numerical model.These findings will broaden our knowledge about the YSWC and associated circulations, improving the predictability of regional climate and providing scientific basis for exploiting and protecting marine resources properly and effectively.