Observations of wind stress and wind profiles over the ocean reported in the literature over the past 10 years are consistent with Charnock's (1955) relation between aerodynamic roughness length (z0) and friction velocity (u*), viz, z0= αu*2/g, with α= 0.0144 and g= 9.81 m s−2. They also imply a von Kármán constant = 0.41±0.025. For practical purposes Charnock's relation may he closely approximated in the range 4&<V<21 m s−1 by a neutral drag coefficient (referred to 10 m) varying with the 10 m wind speed V (m s−1), either by a power law relation CDN(10)×103 = 0.51V0.46or a linear form CDN(10)×103= 0.75+0.067V. Results of recent turbulence sensor comparison experiments suggest that much of the source of data scatter in CDN(V) plots and of the systematic differences between data sets is due to calibration uncertainties associated with sensor performance in the field. The effects (if any) of fetch, wind duration and unsteadiness remain obscured in this experimental data scatter. Vertical transfer o... Abstract Observations of wind stress and wind profiles over the ocean reported in the literature over the past 10 years are consistent with Charnock's (1955) relation between aerodynamic roughness length (z0) and friction velocity (u*), viz, z0= αu*2/g, with α= 0.0144 and g= 9.81 m s−2. They also imply a von Kármán constant = 0.41±0.025. For practical purposes Charnock's relation may he closely approximated in the range 4&<V<21 m s−1 by a neutral drag coefficient (referred to 10 m) varying with the 10 m wind speed V (m s−1), either by a power law relation CDN(10)×103 = 0.51V0.46or a linear form CDN(10)×103= 0.75+0.067V. Results of recent turbulence sensor comparison experiments suggest that much of the source of data scatter in CDN(V) plots and of the systematic differences between data sets is due to calibration uncertainties associated with sensor performance in the field. The effects (if any) of fetch, wind duration and unsteadiness remain obscured in this experimental data scatter. Vertical transfer o...