Observation And Numerical Study Of Circulation Patterns In The Yellow Sea In Summer

The Yellow Sea Cold Water Mass (YSCWM) and its circulation are one of the most outstanding phenomena in the China Sea. However, so far, controversies still remained on the causes and mechanisms of the formation, even on their patterns. In present paper, striking hydrographic features and its circulation patterns of the Southern Yellow Sea were studied, using the data obtained from three cruises in the summer of 2001,2002,2003, especially data from the satellite-tracked drifters, combining with the POM model. By analyzing the data obtained from three cruises in three years, the basic hydrographic features and interannual variability of the Southern Yellow Sea were showed. Some striking hydrographic features indicated that there existed two cold centers in the southern YSCWM; cold water center in the lower layer lied to the east of the upper layer warm water center, and YSCWM turned up along 33.25°N section but was not observed along 32.5°N section. It was proved again that there exists upwelling along the continental slope in summer, and the cold water even could rise to the sea surface. Trajectories and drift velocities of the 33 drifters in three years recorded the upper circulation patterns in southern Yellow Sea, which comprised two-cycle structure: an anti-cyclonic cycle in and an anti-cyclonic cycle out, and demonstrated that such a weak water exchange crossed the front. They provided more powerful evidence for the controversies on the circulation patterns of the YSCWM. Wind-induced currents in the southern Yellow Sea in summer were computed by Ekman formula and POM model, respectively. Through analyzing and contrasting, the main results were as follows: in shallow sea, the wind-induced currents numerically computed by POM model were similar to those computed by Ekman formula; in deep sea, the results computed by Ekman formula was far from the truth, while the wind-induced currents computed by POM model basically showed the actual circulation pattern in the southern Yellow Sea in summer; the faster the wind, the more obvious the difference between two kinds of results. Based on the POM model, the circulation patterns of the southern Yellow Sea in summer were simulated. Three secondary cyclonic systems appeared in the larger counterclockwise circulation. By deploying some points in different sections, the simulated trajectories conformed completely with Euler currents computed by POM model. Then, by tracing ARGOS drifters through POM model, the simulated trajectories were generally similar to those observed in the Yellow Sea. However, for some reasons, such as the shortcomings of the numerical model itself and the special situations during buoys drifting, there existed some differences between the simulated trajectories and the observed ones.