Determining High-Wind Enthalpy Fluxes from Dropsonde Profiles in Tropical Cyclones

Abstract:

In high winds, direct measurements of air-sea fluxes are extremely challenging, and as a result there exist relatively few observationally-based estimates of surface momentum and enthalpy transfer between the air and water. Constraining the corresponding flux coefficients for use in numerical models is paramount to obtaining accurate tropical cyclone forecasts, while their dependence on various physical phenomena such as waves and sea spray remain unresolved. In this work, we use the flux profile technique to estimate surface enthalpy fluxes from dropsonde data spanning 37 different storms, in a manner similar to that used to obtain surface momentum fluxes in previous studies. In particular, we test the robustness of this method using a series of Monte-Carlo-based uncertainty quantification techniques, where uncertain inputs such as the sea surface temperature are varied stochastically. In addition, “virtual dropsonde” profiles extracted from high-resolution large eddy simulations of an idealized tropical cyclone are used to further validate this method for obtaining surface enthalpy fluxes, since all inputs and surface flux parameterizations are known exactly. We conclude that while the flux profile method provides values squarely in the range of previous estimates reported in the literature, these values are only reliable with an error of roughly 100%, particularly at high wind speeds. The causes of this variability and its implications will be discussed.