A study of ocean spray effect on vertical momentum transport in tropical cyclones

In this study, we propose a mathematical model for the ocean spray effect on the vertical momentum transport under a high wind environment associated with hurricanes or severe storms. It is shown that the ocean spray can accelerate the wind due to reduction of turbulence intensity which is caused by a non-uniform vertical distribution of ocean spray in the flow. Our model accounts for the spray concentration dependence from the flow velocity which introduces positive feedback into the flow dynamics. It is demonstrated that the flow acceleration is negligible for the wind velocities below a certain critical value due to the fact that the spray volume concentration is low for such velocities. Spray volume concentration rapidly increases once the flow velocity exceeds this critical value causing a noticeable flow acceleration. The magnitude of the flow acceleration rapidly increases until the spray concentration reaches its maximum value. Our estimations show that the flow velocity may increase up to ~ 30% due to turbulent transport reduction caused by non-uniform vertical spray distribution.

Some of the existing theoretical and numerical investigations predict a significant (up to an order magnitude) flow acceleration caused by the ocean spray presence. The very strong spray-induced flow lubrication predicted by these models has been reexamined in the present work and is determined to be unjustified.

The sensitivity of ocean spray lubrication effect to the theoretical model has been investigated. Specifically we found that the lubrication effect is very sensitive to the influence of spray stratification on the turbulence mixing length. We account for this effect by employing full prognostic equations for turbulent kinetic energy and dissipation rate with no mixing length assumption. An effort to develop a proper spray parameterization based on the theoretical consideration and the results of numerical experiments is undertaken. Consequently, we will incorporate the spray parameterization in the realistic Weather Research and Forecast (WRF) numerical model in order to improve the accuracy of Tropical Cyclone intensity prediction.