On the Effect of Droplets on Momentum Transfer in the Atmospheric Boundary Layer at High Wind Speeds

A possible mechanism for reducing ocean surface aerodynamic drag at extremely high wind speeds, as detected by profiling data from falling GPS probes, is proposed. It is shown that the exchange of momentum between atmospheric air and droplets of spray injected from the ocean surface at high wind speeds leads to a significant deformation of the airflow velocity profile in the atmospheric boundary layer compared to the prediction of the Monin–Obukhov similarity theory (a logarithmic velocity profile). The removal of momentum from the airflow for droplet acceleration leads to a decrease in wind speed and a reduction in the logarithmic derivative of its profile with respect to the vertical coordinate. Furthermore, the use of a logarithmic approximation of the wind speed profile in the profiling method yields effective values of the dynamic velocity, roughness parameter, wind speed at a height of 10 m, and aerodynamic drag that are reduced compared to their true values. When calculating the effective parameters of the turbulent boundary layer, we used the spray generation function due to the bag-breakup fragmentation mechanism. This function describes the sharp increase in droplet number when this mechanism is activated at wind speeds of 30–35 m/s. The calculated values of the turbulent boundary layer effective parameters are in good agreement with experimental data at hurricane-force wind speeds.