Measurement of Turbulent Fluxes and Dissipation Rates in the Coastal Bottom Boundary Layer

Abstract

Abstract : The long-term goals of this project are to quantify turbulence and to understand the mechanisms and implications of turbulent mixing in the bottom boundary layer of the coastal ocean. This project, which is a component of the Coastal Mixing and Optics (CMO) program, includes measurements and analysis aimed at quantifying turbulence and elucidating turbulence dynamics within the bottom boundary layer on the New England continental shelf. The objectives of the measurements are (1) to determine the vertical structure of Reynolds-averaged velocity and temperature; (2) to obtain direct covariance estimates of turbulent momentum and heat fluxes; and (3) to obtain indirect inertial range estimates of dissipation rates for turbulent kinetic energy and temperature variance. The objectives of the analysis are (1) to close approximate budgets for turbulent kinetic energy and temperature variance; (2) to quantify the intensity and scale of vertical mixing; and (3) to test existing turbulence-closure models, which predict the dependence of momentum and heat fluxes on vertical gradients of Reynolds-averaged velocity and temperature. This project differs from previous observational studies of boundary layer dynamics on shelves because it aims at measurements, rather than inferences, of the most important turbulence statistics, and because it resolves not only the classically studied logarithmic wall layer, but also the outer boundary layer, where scaling and model predictions indicate that stable stratification has a major influence on turbulence dynamics, and where rigorous tests of turbulence closure models have not previously been attempted.