Tropical Cyclone Air-Sea Enthalpy Flux Estimates from Dropsonde Profiles

Tropical cyclone models rely heavily on surface flux parameterizations for determining the flux of enthalpy and momentum at the air-sea interface. By doing so, a large burden is placed on the respective transfer coefficients C_K and C_D, since tropical cyclone development and potential intensity have been shown to be highly sensitive to both. Until numerical models are able to capture small-scale surface exchange processes, accurate prediction of these flux coefficients and a full understanding of their behavior with increasing wind speeds is essential, including elucidating which physical processes they are meant to represent. Calculating these parameters, however, is quite difficult in extreme conditions. This work is focused on recent attempts to compute surface fluxes of enthalpy based on mean temperature and moisture profiles obtained from over 2000 individual dropsonde datasets spanning 37 tropical cyclones. By utilizing Monin-Obukhov similarity theory, fits of the mean enthalpy profile produce surface enthalpy fluxes up to 10-meter wind speeds of 50 m/s. By using the Reynolds sea surface temperature analysis product, C_K is estimated from the enthalpy flux and is found to be in the same broad range as C_K predicted by other methods. More importantly, however, scaling of the surface enthalpy flux with wind speed reveals an important signature of the effects of sea spray. This evidence of spray, a comparison with existing measurements of enthalpy flux, and a discussion of the sources of uncertainty will be included.