Impact of Surface Waves on Wind Stress under Low to Moderate Wind Conditions

Abstract

<p>The impact of ocean surface waves on wind stress at the air–sea interface under low to moderate wind<br>conditions was systematically investigated based on a simple constant flux model and flux measurements<br>obtained from two coastal towers in the East China Sea and South China Sea. It is first revealed that the<br>swell-induced perturbations can reach a height of nearly 30m above the mean sea surface, and these perturbations<br>disturb the overlying airflow under low wind and strong swell conditions. The wind profiles severely<br>depart from the classical logarithmic profiles, and the deviations increase with the peak wave phase speeds. At<br>wind speeds of less than 4 m/s, an upward momentumtransfer from the wave to the atmosphere is predicted,<br>which is consistent with previous studies. A comparison between the observations and model indicates that<br>the wind stress calculated by the model is largely consistent with the observational wind stress when considering<br>the effects of surface waves, which provides a solution for accurately calculating wind stress in ocean<br>and climate models. Furthermore, the surface waves at the air–sea interface invalidate the traditional<br>Monin–Obukhov similarity theory (MOST), and this invalidity decreases as observational height increases.</p>