The seasonal evolution of the Yellow Sea Cold Water Mass Circulation: Roles of fronts, thermoclines, and tidal rectification

The Yellow Sea Cold Water Mass (YSCWM), surrounded by thermocline and fronts, is one of the most notable hydrological characteristics of the Yellow Sea (YS) in the summer. Temperature structure at the boundary of the YSCWM drives the Yellow Sea Cold Water Mass Circulation (YSCWMC). However, the 3D structure of YSCWMC remains unclear. The position, seasonal evolution, and dynamical mechanisms of the YSCWMC were examined by observations and high-resolution numerical model. It was found that the core of the YSCWMC is located at the junction of the fronts and the thermocline during the summer. Furthermore, the YSCWMC exhibits remarkable seasonal variations characterized by a progressive shrinking and deepening dependence on the position and strength of the fronts and thermocline. The YSCWMC is geostrophic at the basin scale, with the barotropic pressure term determining the direction of the circulation and the baroclinic pressure term controlling the vertical structure of the circulation. Fronts yield a baroclinic effect in the thermal field and affect the sea surface elevation in the barotropic process. Therefore, fronts are crucial to the formation of the YSCWMC. Nevertheless, under conditions of steep topography, tidal rectification is comparable to the frontal contribution to the circulation.