Observations of Turbulent Fluxes and Turbulence Dynamics in the Ocean Surface Boundary Layer

Gregory Gerbi, Ph.D., 2008
John Trowbridge, Advisor

This study presents observations of turbulence dynamics made during the low winds portion of the Coupled Boundary Layers and Air-Sea Transfer experiment (CBLAST-Low) in the ocean surface boundary layer. Observations include turbulent fluxes, turbulent kinetic energy, and the length scales of flux-carrying and energy-containing eddies. The observations of turbulent fluxes allowed the closing of heat and momentum budgets across the air-sea interface. The flux-carrying eddies are similar in size to those expected in rigid-boundary turbulence, but energy-containing eddies are smaller than those in rigid-boundary turbulence. The observations confirm previous speculation that surface wave breaking provides a surface source of turbulent kinetic energy that dissipates as it is transported to depth. A model that includes the effects of shear production, transport, and dissipation is able to reproduce the enhancement of turbulent kinetic energy near the ocean surface. The ocean surface boundary layer is observed to have small but finite temperature gradients that are related to the boundary fluxes of heat and momentum, as assumed by closure models. However, the turbulent diffusivity of heat in the surface boundary layer is larger than predicted by rigid-boundary closure models. This discrepancy can be explained by the addition of wave breaking to the rigid-boundary model.