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

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