The scaling of velocity fluctuations in the surface mixed layer

Abstract

Turbulent velocity fluctuations in the upper portions of the wind-driven mixed layer of oceans or lakes appear to have a velocity scale proportional to the friction velocity and a length scale proportional to the distance below the free surface, as is usual in shear flows near a boundary. A number of one-dimensional velocity spectra have been measured in aquatic mixed layers, and these spectra, when they are scaled with the surface stress and the distance from the free surface, have been compared with turbulent boundary layer measurements. The good agreement suggests that the surface wave orbital velocities act merely as ‘inactive’ motions and do not interfere with the lower-frequency stress-carrying eddies.