Effects of Breaking and Non‐Breaking Surface Wave Mixing on the Changjiang River Plume Dynamics in Summer

Abstract

AbstractA wave‐current coupled model is implemented to investigate the impact of breaking and non‐breaking surface wave mixing on the structure and dynamics of the Changjiang River plume. Two main non‐breaking wave mixing schemes, modifying the turbulent viscosity directly versus adding wave‐induced turbulence production in the turbulence closure model, are incorporated to the Coupled Ocean‐Atmosphere‐WAVE‐Sediment Transport modeling system. Surface wave mixing typically thickens the plume and traps more freshwater in the near‐ and mid‐field regions. The surface turbulent kinetic energy produced by breaking waves corresponds to small wave energy input in fair weather conditions and has a moderate effect on the Changjiang River plume. In contrast, the addition of non‐breaking wave mixing enhances the turbulent viscosity roughly an order of magnitude in the surface layer. Simulations with non‐breaking wave mixing improve the representation of the plume structure compared to models without wave mixing or with only breaking wave mixing. The Changjiang River plume exhibits a north‐south asymmetry in both salinity and current field in summer. Further adding the non‐breaking wave mixing reduces the surface Ekman velocity and lowers the offshore plume expansion rate through interactions between the upwelling favorable winds and the Ekman layer depth. The resulting adjustment to the internal pressure gradient enhances the buoyancy current and magnifies the asymmetric structure of the Changjiang River plume in summer. While the two non‐breaking wave mixing schemes are conceptually different, our modeling experiments suggest that they have similar effects on the plume structure.