Momentum transfer and foam production via breaking waves in hurricane conditions

Abstract: Generated under hurricane conditions, a slip layer composed of foam, bubble emulsion, and spray determines the behavior of the surface drag with wind speed. This study enables us to estimate foam's contribution to this behavior. A logarithmic parametrization of surface drag is introduced, wherein the effective roughness length of the underlying surface is decomposed into three fractional roughness lengths. These correspond to the foam-free area (as determined by laboratory data, which includes the effects of spray and bubble emulsion) and ocean areas covered by whitecaps and streaks, each weighted by their respective coverage coefficients. A key concept of this approach is the use of well-established experimental bubble-size spectra produced by breaking surface waves to obtain the effective roughness length. This method provides a fair correlation of the logarithmic parametrization of surface drag against wind speed with a wide class of respective experimental data. Additionally, this approach estimates the hurricane's potential intensity, demonstrating reasonable agreement with experimental findings.