Impact of the Waves on the Sea Surface Roughness Length under Idealized Like-Hurricane Wind Conditions (Part II)

Abstract

In this study the effect of the surface waves over sea surface roughness ( z 0 ) and drag coefficient ( C D ) is investigated by combining an ocean wave model and a simplified algorithm, which estimates z 0 and C D with and without dependence on the sea state. This investigation was possible from several numerical simulations with the Wave-Watch-III (WW3) model for complex wind conditions. The numerical experiments were performed for idealized like-hurricanes with different translation speed (0, 5 and 10 m/s) and maximum wind speed (MWS) at the centre (35, 45 and 55 m/s). It is observed that z 0 and C D are strongly dependent on the sea state, via substantial modification in Charnock parameterization ( z ch ). As the hurricane translation speed increases more discrepancies in z 0 and C D are observed in opposite quadrants around the region of MWS. As for instance, higher, longer and older (or more developed) waves, located in the front-right quadrant, produce lower values of z 0 and C D . In the rear-left quadrant, where the waves are lower, shorter and younger (or less developed), higher values of z 0 and C D are observed. In addition the difference between values on opposite quadrants increases as the hurricane intensity increases, showing the hurricane intensification dependence. Interesting aspects are observed in scatter plotting wave age versus Charnock coefficient. It is also observed that z ch , which has a constant value of 0.0185, is modified by the sea state, where young waves produce higher values of z ch , while old waves are related to lower values of z ch when compared with z ch without dependence on sea state.