The enthalpy (sensible and latent heat) exchange processes within the surface layers at an air-water interface have been examined in 15-m wind-wave tunnel at the Rosenstiel School of Marine and Atmospheric Science, University of Miami. The objective of experiments was to reveal the physics of the processes of the turbulent transfer of heat under controlled conditions, thereby advance our understanding of scalar exchange processes at the air-water interface, in particular in high winds.

The turbulent flux of moist enthalpy (the flux driven by differences in temperature and water vapor density between the surface and the air) was measured indirectly by the ²Calorimetric² method (the measurement of the amount of heat lost by warmer water body to the air). Measurements yielded 72 mean values of fluxes and bulk variables in wind speed (referred to 10 m) range from 0.6 to 39 m/s, covering a full range of aerodynamic conditions from smooth to fully rough. The water–air temperature difference range explored was 1.3 to 9.2 °C.

Meteorological variables and bulk enthalpy transfer coefficients, measured at 0.2–m height, were adjusted to neutral stratification and 10–m height following the Monin–Obukhov similarity approach. Characteristic behavior of the enthalpy transfer coefficient as the surface condition goes from aerodynamically smooth to rough was revealed. In the high wind regime, the enthalpy coefficients did not show significant variation with wind speed. The ratio of the bulk coefficients of enthalpy and momentum was estimated to evaluate the hypothesis that the ratio of order 1 are required for intense hurricanes to form.

The calorimetric measurements gave reliable estimates of enthalpy flux from the air–water interface, but the moisture gained in the lower air from evaporation of spray over the rough water remained uncertain, stressing the need for flux measurements along with simultaneous spray data to quantify spray¢s contribution to the turbulent air-water enthalpy fluxes.