A numerical study on the density driven circulation in the Yellow Sea Cold Water Mass

Abstract

The circulation of Yellow Sea Cold Water Mass (YSCWM) in the Southern Yellow Sea is investigated using a diagnostic 2D MITgcm model. The resolution of the computational grid is 900 m in the horizontal and 2 m in the vertical where an initial temperature distribution corresponding to a typical measured Yellow Sea Cold Water Mass was applied. The existence of YSCWM that causes fluid density difference, is shown to produce counter-rotating cyclonic horizontal eddies in the surface layer: the inner one is anti-cyclonic (clockwise) and relatively weaker (8–10 cm s−1) while the outer one is cyclonic (anti-clockwise) and much stronger (15–20 cm s−1). This result is consistent with the surface pattern observed by Pang et al. (2004), who has shown that a mesoscale anti-cyclonic eddy (clockwise) exists in the upper layer of central southern Yellow Sea, and a basin-scale cyclonic (anticlockwise) gyre lies outside of the anti-cyclonic eddy, based on the trajectories and drifting velocities of 23 drifters. Below the thermocline, there is an anti-cyclonic (clockwise) circulation. This complex current eddy system is considered to be capable of trapping suspended sediments and depositing them near the front between YSCWM and the coastal waters off the Subei coast, providing an explanation on the sediment depth and size distribution of mud patches in the Southern Yellow Sea. Moreover, sensitive test scenarios indicate that variations of bottom friction do not substantially change the main features of the circulation structure, but will reduce the bottom current velocity, increase the surface current velocity and weaken the upwelling around the frontal area.