Wave-Driven Langmuir Turbulence in Coastal Oceans: Observations, Simulations, and Implications for Transport

Abstract:

Surface gravity wave-driven Langmuir turbulence (LT) transports momentum, energy, and material throughout the ocean surface boundary layer (OSBL). LT is characterized by counter-rotating roll vortices (Langmuir circulations) with relatively strong, persistent near-surface convergence zones and downwelling regions. In the open ocean, these characteristics have been observed and successfully modeled utilizing a turbulence-resolving large eddy simulation (LES) approach based on the wave-averaged Craik-Leibovich equations. Observations and simulations indicate that LT facilitates transport throughout the OSBL, increases buoyancy entrainment at the OSBL base, and deeply submerges buoyant tracers. The focus of this presentation is on under-studied LT in a coastal ocean environment. Relatively recent coastal observations and simulations indicate that pairs of Langmuir circulation cells extend horizontally over length scales comparable to multiple water depths. Furthermore, Langmuir circulations may effectively couple the OSBL with the bottom boundary layer by filling the whole water column. In a coastal ocean environment, strong tidal currents and wind-wave misalignment may weaken and disrupt Langmuir circulations. LES results indicate that LT controls vertical and horizontal material dispersion processes, confirming that LT plays a key role in coastal transport dynamics.