ON THE DEPENDENCE OF SEA-SURFACE ROUGHNESS ON WIND-WAVES

The influence of wind waves on the momentum transfer (wind stress) bet ween the atmosphere and sea surface was studied using new measured dat a from the RASEX experiment and other datasets compiled by Donelan et al. Results of the data analysis indicate that errors in wind friction velocity u of about +/- 10% make it difficult to conclude on the tre nd in z(ch) using measured data from a particular dataset. This proble m is solved by combining different field data together. This gives a t rend of decreasing z(ch) with wave age, expressed as: z(ch) = 1.89(c(p )/u)(-1.59). Furthermore, it Is shown that calculations of the wind f riction velocities using the wave-spectra-dependent expression of Hans en and Larsen agrees quite well with measured values during RASEX. It also gives a trend in Charnock parameter consistent with that found by combining the field data. Last, calculations using a constant Charnoc k parameter (0.018) also give very good results for the wind friction velocities at the RASEX site.