The wave coherent stress and turbulent structure over swell waves

Abstract

The generation of ocean surface waves by wind has been studied for a century, giving rise to wave forecasting and other crucial applications. However, the reacting force of swell waves on the turbulence in the marine Atmospheric Boundary Layer (ABL) remains unknown partly due to the unclear magnitude and profile of Wave Coherent (WC) stress. In this study, the intersection frequency between the energy-containing range and inertial subrange range in the turbulent spectra is identified based on the Attached Eddy Model (AEM), as the intersection modulated by swell wave could help to comprehend the physical process between the ocean surface wave and the marine ABL. Using observations from a fixed platform located in the South China Sea, this study shows that the intersection when the WC stress accounts for a lower proportion of the total wind stress (< 10%) follows U/(2πz) given by AEM, here U is wind speed, z is height. While the intersection depends on the drag coefficient of WC stress for the case when WC stress accounts for a large part of the total wind stress (> 10%). Considering the unclear magnitude and profile of WC stress, this study derives a new function to depict the WC stress.