Wind-wave stabilization by a foam layer between the atmosphere and the ocean

TL;DR

This paper investigates how a foam layer between the atmosphere and ocean can reduce wind-driven wave activity by stabilizing the water surface through Kelvin-Helmholtz instability analysis, potentially explaining decreased momentum transfer.

Contribution

It introduces a three-fluid model of air, foam, and water to estimate foam layer thickness needed for effective stabilization of the ocean surface.

Findings

Thin foam layers can significantly stabilize the water surface.

The foam layer shifts instability to smaller wavelengths, reducing roughness.

This mechanism may explain observed decreases in wind drag on the ocean.

Abstract

The study is motivated by recent findings of the decrease in the momentum transfer from strong winds to sea. The Kelvin-Helmholtz instability (KHI) of a three-fluid system of air, foam and water is examined within the range of intermediately short surface waves. The foam layer thickness necessary for effective separation of the atmosphere and the ocean is estimated. Due to high density contrasts in the three-fluid system, even a relatively thin foam layer between the atmosphere and the ocean can provide a significant stabilization of the water surface by the wavelength shift of the instability towards smaller scales. It is conjectured that such stabilization qualitatively explains the observed reduction of roughness and drag.