Potential low bias in high-wind drag coefficient inferred from dropsonde data in hurricanes

One method for estimating air-sea momentum transfer in high winds is the flux-profile method, which infers surface momentum fluxes and the corresponding drag coefficient from mean velocity profiles obtained from either dropsondes or meteorological towers, under the assumption that the boundary layer wind profile at low altitudes exhibits a logarithmic profile with height.

In this study, we use dropsonde data from reconnaissance aircraft, as well as "virtual sondes" from a turbulence-resolving simulation of an intense tropical cyclone, to critically analyze the diagnosis of drag coefficient C-D at hurricane-force wind speeds. In particular, the "rolloff" of the drag coefficient, where C-D decreases at 10-m wind speeds > 35 m s(-1), is called into question based on uncertainty due to relatively low sample size and a lack of robustness of the flux-profile method at high winds.