Impact of the Waves on the Sea Surface Roughness under Uniform Wind Conditions: Idealized Cases for Uniform Winds (Part I)

Abstract

The effect of the surface gravity waves over sea surface roughness length ( z 0 ) is investigated from several idealized numerical experiments with the Wave-Watch-III (WW3) model. The WW3 model is combined with a simplified model to estimate z 0 , C D , u * and U 10 as function of the sea state. The impacts related to the presence of the ocean waves over z 0 are obtained from conditions of growing (young waves) and mature seas (old waves). The wave spectrum is obtained from WW3 model for each idealized simulation under uniform wind conditions. Uniform wind experiments range from 15 to 45 m/s. The simplified algorithm determines z 0 , C D , u * and U 10 for cases of young waves, old waves and by the Charnock method. The results show that when the ocean is characterized by young waves, both z 0 and C D (drag coefficient) increase while U 10 is reduced. In Charnock case, the values of z 0 , C D and U 10 have no dependence with the presence of gravity waves. Experiments using winds higher than 30 m/s result in young waves’ C D values higher than the C D value for old waves. Even for young waves C D values are high for cases of strong winds. The results also show that in experiments using winds higher than 30 m/s the dependence between C D and wave age becomes stronger, which is in accordance with other studies.