An Assessment of the Flux Profile Method for Determining Air-Sea Momentum and Enthalpy Fluxes from Dropsonde Data in Tropical Cyclones

An analysis of the reliability of using dropsonde profile data to compute surface flux coefficients of momentum and heat is performed. Monin-Obukhov (MO) similarity theory forms the basis for the flux profile method, where mean profiles of momentum, temperature, and moisture are used to estimate surface fluxes, from which bulk flux coefficients can then be determined given surface conditions. The robustness of this method is studied in terms of its sensitivity to internal, method-based parameters, as well as the uncertainty due to variability in the measurements and errors in the estimates of surface conditions, particularly sea surface temperature. In addition, "virtual sondes'' tracked through a high-resolution large-eddy simulation of an idealized tropical cyclone are used to evaluate the flux profile method's ability to recover known surface flux coefficients given known, prescribed surface conditions; this provides a test of whether or not MO assumptions are violated and under which regions they hold. Overall, it is determined that the flux profile method is only accurate within 50% and 200% for the drag coefficient C-D and enthalpy flux coefficient C-K, respectively, and thus is limited in its ability to quantitatively refine model estimates beyond typically used values. Factors such as proximity to the storm center can cause significant errors in both C-D and C-K.