Simultaneous Observations of Turbulent Reynolds Stress in the Ocean Surface Boundary Layer and Wind Stress over the Sea Surface

Abstract

This study used high-frequency acoustic instruments mounted on an offshore observation platform to obtain simultaneous in situ measurements of sea surface winds and ocean currents. The acquired data were used to compare quantitatively the turbulent Reynolds stress in the ocean surface boundary layer (OSBL) and the wind stress over the sea surface. During the study period (∼10 d), the sea state was largely dominated by swell and breaking wind waves. The eddy covariance method was used to estimate the two stresses. A combination of the synchrosqueezed wavelet transform (SWT) method and a moving average was employed for wave-turbulence decomposition of the oceanic velocities. Results showed that the turbulent Reynolds stress in the OSBL is affected greatly by surface gravity waves and that it scales with the wave characteristics. Direct comparison revealed that the turbulent Reynolds stress in the OSBL could be larger than the wind stress in certain circumstances, which differs from the traditional view that the former cannot be greater than the latter. In certain extreme cases, their ratio can be up to one order of magnitude. Therefore, we conclude that surface waves can enhance significantly the turbulent Reynolds stress in the OSBL.