Representing wave effects on currents
Leonel Romero, Delphine Hypolite, James C. McWilliams
Abstract
We describe a new framework to represent wave effects on currents, including several approximations (Stokes drift, Bernoulli head, and quasi-static pressure) and a parameterization of the vertical mixing due to wave breaking. The framework improves over existing methods not limited by water depth or monochromatic assumptions. The approximations are validated with spectra and current profiles from a model configuration in Southern California. The Stokes drift approximation uses two scales accounting for broadband spectra, including mixed wind-sea and swell. The Stokes drift is estimated iteratively, constrained by the surface drift velocity and Stokes transport, being more efficient while giving smaller errors compared to a spectrum reconstruction approach. One-month-long hydrostatic ocean model solutions at 270 m horizontal grid resolution show that waves have relatively small impacts on the mean circulation and mesoscale current variability near the surface. Waves increase the vorticity and divergence variance near the surface when the turbulent Langmuir number is small.