Effect of wind waves on air’sea gas exchange: proposal of an overall CO₂ transfer velocity formula as a function of breaking-wave parameter

Abstract

A new formula for gas transfer velocity as a function of the breaking-wave parameter is proposed basedon correlating gas transfer with whitecap coverage. The new formula for gas transfer across an air—seainterface depends not only on wind speed but also on wind-wave state. At the same wind speed, ahigher gas transfer velocity will be obtained for a more developed wind-sea, which is represented by asmaller spectral peak frequency of wind waves.We suggest that the large uncertainties in the traditionalrelationship of gas transfer velocity with wind speed be ascribed to the neglect of the effect of windwaves. The breaking-wave parameter can be regarded as a Reynolds number that characterizes theintensity of turbulence associated with wind waves in the downward-bursting boundary layer (DBBL).DBBL provides an effective way to exchange gas across the air—sea interface, which might be relatedto the surface renewal.