Vertical Profiles of Wave–Coherent Momentum Flux and Velocity Variances in the Marine Atmospheric Boundary Layer

The wave--coherent momentum flux and velocity variances are investigated using a theoretical model and open ocean measurements. The spectrum--integrated wave--coherent (SIWC) momentum flux and velocity variances decay roughly exponentially with height. The exponential decay coefficients of the SIWC momentum flux and velocity variances decrease with increasing peak wave number. The phases of the wave--coherent horizontal/vertical velocity fluctuations are approximately 180^o/90^o under waves with wind--wave angle |α| < 90^o, respectively. In general, the ratio of the SIWC momentum flux to the total momentum flux under swell conditions is higher than that under wind wave conditions at the same height. At a height of 9.9 m, the SIWC vertical/horizontal velocity variances can exceed 30%/10% of the total vertical/horizontal velocity variances at high wave ages, respectively. The impact of SIWC momentum flux on wind profiles is determined mainly by the surface SIWC momentum flux ratio, the decay coefficient of the SIWC momentum flux, and the sea surface roughness length, with the first two factors being dominant. The results of this study suggest a methodology for parameterizing the SIWC momentum flux and the total momentum flux over the ocean. This results is important for simulating the marine atmospheric boundary layer and should be used in model development.