A Practical Bi-parameter Formula of Gas Transfer Velocity Depending on Wave States

Copyright©The Oceanographic Society of Japan/TERRAPUB/Springer where u∗ is the friction velocity of the air, ρa is air density. U10 is the wind speed at 10 m height above the sea surface in neutral stratification condition; CD is the drag coefficient. Many studies have shown that air-sea exchange is regulated by turbulence associated with wind and wind waves at the air-sea interface (Jähne et al., 1987; Komori et al., 1993). However, it is often difficult to find a suitable parameter that is robust enough to describe turbulence intensity in natural environmental conditions. Alternatively, wind speed has been mostly chosen as the parameter since wind is the primary forcing of the air-sea boundary layer and easy to obtain from routine observational data. In order to extrapolate fluxes over long time and space scales, gas transfer velocities are usually assumed to be a function of wind speed alone (Liss and Merlivat, 1986; Wanninkhof, 1992; Nightingale et al., 2000a, b; Sweeney et al., 2007). These relationships show a wide range of scatter, especially at high wind speed, and give rise to large discrepancies in the estimation of air-sea gas fluxes. Such a scatter could be caused by the uncertainties in the measurement of gas transfer velocities and in the determination of the wind speed. It could also be caused by other factors that influence gas transfers, but have not been taken into account. For instance, in addiA Practical Bi-parameter Formula of Gas Transfer Velocity Depending on Wave States