24 / 2023-07-24 15:07:50

The role of wind-wave-current coupling on the merge of surface and bottom boundary layers in the coastal ocean

coastal ocean, surface boundary layer, bottom boundary layer, merge, Langmuir Supercells

The turbulent flow in the shallow-water coastal region controls boundary structure and substance mixing in this layer, playing a crucial role in processes such as air-sea exchanges, diapycnal transport, and sediment resuspension in the coastal ocean. Oceanic boundary layers in coastal regions are driven by external forces such as wind, waves, and currents, resulting in a highly complex dynamical system with multiple active mixing layers. Canonically, the two most common boundary layers in the ocean are the wind-wave-driven surface boundary layer (SBL), and the current-shear-driven bottom boundary layer (BBL). Recent studies have shown that the SBL and BBL in shallow water can have strong interactions and merge into one layer. The merged layer is occupied by a specific type of turbulence, Langmuir Supercells. However, the physical mechanisms of such a process have yet to be revealed. In this study, we use the large eddy simulation (LES) to investigate the evolution of SBL and BBL in the coastal area and the merging processes. LES can reproduce high-fidelity turbulent flow with extremely high spatial and temporal resolutions, directly resolving interactions between two boundary layers in the coastal ocean and the turbulent mixing processes. The coherent flow patterns within SBL and BBL before and after merging are shown. And the relation between the merge and the external forcings is characterized.