1055 / 2024-09-20 10:03:57

Structure and dynamics of the middle layer circulation in the northern South China Sea

Striations,Nonlinear Dynamics,Deep ocean circulation,Potential Vorticity

In ocean circulation, the middle layer zonal velocity typically exhibits meridional alternating eastern and western flow structures, considerably narrower than surface wind-driven circulations. The generation of those jets could lead to an energy inverse cascade, which contributes to the eddy interactions after considering the beta effect. Utilizing the Argo float temperature, salinity, and trajectory data, this study investigates the subsurface zonal velocity structure above a reference depth of 1200 m in the northern South China Sea (SCS). The zonal geostrophic velocity exhibits quasi-zonal eastward/westward altering flows in the middle layer roughly between 200-800 m. The spatial distribution of those jets corresponds well with the high eddy kinetic energy, hinting at turbulent energy transferring from the eddy to the mean flow. The turbulent Sverdrup balance mechanism explains the formation of the quasi-zonal striations, highlighting the crucial role of eddy nonlinear interaction. Besides, the southwest-northeast tilt of the striation-like structure is attributed to the topographic beta effect.