Air-sea thermodynamic fluxes in high winds and a signature of spray effects

Due to the difficulties of making accurate measurements of thermodynamic fluxes high winds, little is known about the routes through which heat and moisture are transferred at the air-sea interface in winds exceeding 20 m/s. It has been repeatedly postulated using bulk microphysical models that spray-mediated fluxes at the ocean surface contribute significantly to the total transfer of sensible and latent heat from the ocean, however observational or experimental confirmation of this phenomenon has been difficult to achieve. The research presented here therefore has two aims: (1) to provide additional estimates of enthalpy fluxes within tropical cyclones and (2) to show, for the first time, evidence of spray-mediated fluxes using existing high-wind measurements.

The first task listed above is done by analyzing over 2000 dropsonde datasets to create mean vertical profiles of thermodynamic quantities, and relating these mean profiles to surface fluxes using Monin-Obukhov similarity theory. Several approximations must be made in this process but estimates of the enthalpy bulk flux coefficient are similar to those obtained using other techniques. For the second task, we observe the effects of spray by computing the power-law scaling coefficient of the total enthalpy flux as a function of 10-meter wind speed. In agreement with model predictions, a stronger dependence of enthalpy flux with wind speed is found in measurements taken from within tropical cyclones than in cases where spray would not be expected to play a large role. The limitations and implications of these findings will be discussed.