Parameterization of air-ocean gas transfer

A renewal-type model, based on the physics of a molecular sublayer, allows the derivation of parameters to describe air-ocean gas transfer and the temperature difference across the cold film. The 'surface Richardson number' controls transition from convective instability to wind induced instability ('rollers' on breaking wavelets) and the Keulegan number controls transition from the regime of 'rollers' to long-wave breaking. Critical value of the 'surface Richardson number' and of a nondimensional constant can be evaluated by comparison of parameters describing the cold film with field data. Critical value of the Keulegan number can be determined from the wind speed at which long-wave breaking appears. The parameterization of air-ocean gas transfer predicts a constant value for the gas transfer coefficient at calm and low wind speed conditions (depending on the surface heat flux). The coefficient rises as a function of friction velocity at moderate wind speeds, and decreases inversely proportional to a half-power of the friction velocity at large wind speeds.