Submesoscale Eddy Dynamics and Energy Transfer in a Tidally Dominated Coastal System

The southern coast of Korea is characterized by a complex Rias coast and a barotropic flow regime dominated by strong tides. Under the influence of tidal forcing, complex current patterns develop regularly, leading to the generation of coastal eddies with spatial scales ranging from 0.1 to 10 km. These submesoscale eddies serve as an intermediary between mesoscale dynamics and small-scale turbulence, playing an important role in energy transfer. The goal of this study is to understand the dynamics of eddies observed during a field campaign near the Yokji region and Nodae Island using an eddy-resolving numerical model (with a grid resolution of 30 m). A numerical hydrodynamic model for the region was developed by the Deflt3D model and validated using Acoustic Wave and Current profiler data, velocity fields estimated from unmanned aerial vehicle imagery, and Sentinel-2 true-color imagery. To characterize eddy generation and interaction processes, the barotropic vorticity diagnostics for the depth-integrated flow are used. The local dynamics of submesoscale eddies highlight that the nonlinear advection is the leading local source of vorticity over the study area, followed by secondary contributions from bottom pressure torque and bottom drag curls interacting with topography. We employed a coarse-graining approach to estimate multiscale energy fluxes and kinetic energy transfer. The analysis suggests a tendency for localized upscale energy transfer into adjacent larger-scale background current during the eddy dissipation phase, and that barotropic instability near the cape is a potential contributor to the observed eddy generation. This framework will offer broader applicability for understanding submesoscale energetics and instability processes in tidally dominated shallow coastal systems.