On the exchange of momentum over the open ocean

This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments andwind profiles were collected during three of them. The objective of the investigation is to improve parameterizations of the surface roughness and drag coefficient used to estimate the surface stress from bulk formulas. Specifically, the CoupledOcean–Atmosphere Response Experiment (COARE) 3.0 bulk flux algorithm is refined to create COARE 3.5. Oversea measurements of dimensionless shear are used to investigate the stability function under stable and convective conditions. The behavior of surface roughness is then investigated over a wider range of wind speeds (up to 25m s21) and wave conditions than have been available from previous oversea field studies. The wind speed dependence of the Charnock coefficient a in the COARE algorithm is modified to a5mU10N 1 b, where m 5 0.017m 21 s and b 5 20.005. When combined with a parameterization for smooth flow, this formulation gives better agreement with the stress estimates from all of the field programs at all winds speeds with significant improvement for wind speeds over 13m s21. Wave age – and wave slope–dependent parameterizations of the surface roughness are also investigated, bu