On the Dependence of Sea Surface Roughness on Wind Waves

Abstract

The influence of wind waves on the momentum transfer (wind stress) between the atmosphere and sea surface was studied using new measured data 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 trend in z_ch using measured data from a particular dataset. This problem is solved by combining different field data together. This gives a trend 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 friction velocities using the wave-spectra-dependent expression of Hansen 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 Charnock parameter (0.018) also give very good results for the wind friction velocities at the RASEX site.