Structure and instability of the Ekman spiral in the presence of surface gravity waves

Abstract

The low-frequency Ekman response in the interior of unstratified mixed layers is much less sheared than is predicted using eddy viscosity models that reproduce the temperature structure. However, the response is more sheared than predicted by models that parameterize the mixed layer as a slab. For some realistic conditions, the Ekman spiral predicted by assuming small-scale diffusion alone is strongly unstable to Langmuir cells driven by wave-current interaction. Finite-difference code runs that include infinite-length trains of surface gravity waves qualitatively explain the reduction in shear within the mixed layer relative to that predicted by small-scale mixing. -from Authors