Wave Phase based Conditional Sampling of Reynolds Stresses in the Coastal Ocean Bottom Boundary Layer

The paper discussed methods for conditionally sample Reynolds stresses measured in the bottom boundary layer of the coastal ocean based on the wave phase. Since wave contamination prevents direct calculation of stresses, PIV data is used for estimating the stresses from the second order structure functions of the spatial velocity distributions. Hilbert transforms of pressure signal and spatially averaged velocity are used for determining the wave phase. For most cases, a phase mismatch occurs when the wave amplitude is small or when the turbulence is high. The data are then sub-sampled, keeping only points for which the phase difference is less than 35°. Such sub-sampling has little impact on the Reynolds stresses. Conditional sampling shows that all the Reynolds stresses vary with wave phase, but the variations of the shear stress are particularly high. Except for a consistent minimum in 〈u′u′ 〉 at the phase of maximum wave induced velocity, there are significant differences between trends of data recorded at different elevations and/or times.