Turbulence intensities and bulk coefficients in the surface layer above the sea

The structure of the atmospheric surface layer above the sea is analysed from aircraft turbulence measurements. The data are issued from two experiments performed in 1990 above the Mediterranean sea: Crau and PYREX, and correspond to moderately unstable conditions and to wind velocities ranging from 6 to 20 m/s. Low-altitude straight and level runs were used to compute the variances of the wind components, as well as of the temperature and moisture. Their dependence on the stability index —z/L is analysed. The turbulent fluxes of momentum, sensible heat and latent heat, calculated by the eddy-correlation technique, are used to estimate the neutral bulk coefficients: drag coefficient, Stanton number and Dalton number. The neutral drag coefficient clearly exhibits a dependence on the windspeed, which could be well fitted by the Charnock relation, with a constant of 0.012.