Drag coefficient for the air-sea exchange: foam impact in hurricane conditions

TL;DR

This paper introduces a physical model to estimate how foam coverage on the sea surface affects the drag coefficient during hurricanes, improving understanding of air-sea interactions in storm conditions.

Contribution

The study presents a novel model that partitions the sea surface into foam-covered and foam-free areas to estimate the drag coefficient's variation with wind speed in hurricanes.

Findings

Model agrees with field measurements of wind speed profiles.

Foam coverage significantly influences the effective drag coefficient.

Dependence of C_d on U10 is accurately captured by the model.

Abstract

A physical model is proposed for the estimation of the foam impact on the variation of the effective drag coefficient, C_d, with reference to the wind speed U10 in stormy and hurricane conditions. In the present model C_d is approximated by partitioning the sea surface into foam-covered and foam-free areas. Based on the available optical and radiometric measurements of the fractional foam coverage and the characteristic roughness of the sea-surface in the saturation limit of the foam coverage, the model yields the resulting dependence of C_d vs U10. This dependence is in fair agreement with that evaluated from field measurements of the vertical variation of the mean wind speed.