Effects of Wind Forcing Interval on Near-Inertial Waves and Vertical Mixing in the shelf seas around Korea

The dynamical and thermal properties of the upper ocean are significantly influenced by wind forcing at the sea surface. In this study, numerical simulations with wind forcing applied at different time intervals (1, 3, 6, 12, and 24 hours) were conducted to analyze the heat budget of the surface mixed layer (ML) in the stratified Yellow Sea. The goal was to identify the physical processes modifying ML characteristics and determine the optimal temporal resolution of wind forcing to accurately simulate these processes. During summer, strong energy densities in the near-inertial and internal tide frequency bands drive vertical heat diffusion and entrainment at the ML base. Higher temporal resolution in wind forcing amplifies the activity of near-inertial waves (NIWs) in the upper thermocline, enhancing vertical mixing. This increased mixing thickens the ML, raises its salinity, and lowers its temperature, resulting in greater net heat flux into the surface layer. Consequently, high-frequency wind forcing leads to a reduction in ML temperature in the central Yellow Sea. Wind forcing intervals of 6 hours or less are essential to simulate saturated energy densities of inertial oscillations and vertical mixing in the thermocline at depths of 10–30 m. The enhanced NIWs induced by high-frequency wind variability are expected to transport more nutrients and CO2 from the subsurface to the thermocline and upper ocean layers, underscoring the ecological and biogeochemical impacts of wind forcing resolution in shelf seas.