Evaluating Wind Gust Parameterization in the COARE Air-Sea Flux Algorithm

Saildrone Ucrewed Surface Vehicle (USV) measurements in the Tropical Pacific Ocean are used to evaluate the gustiness parameterization in the Coupled Ocean-Atmosphere Response Experiment version 3.6 (COARE 3.6) bulk air-sea flux algorithm. Typically, the amplitude of the vector mean wind at 10-min or longer time scales is input to the algorithm, but this input is not always representative of variations in the wind field, especially over long averaging intervals. The COARE algorithm adds wind variance to the vector mean wind through a gustiness parameter Ug. Gustiness is parameterized as an empirical relation proportional to the convective velocity scale under the assumption that convective eddies drive gustiness. The 1-minute means of meridional wind v and zonal wind u reported by Saildrone enable the calculation of both the full scalar wind (including its variance, i.e. its natural gustiness) and the vector mean wind. As a result, the wind variance that is traditionally missing from the vector mean wind can be directly calculated from these Saildrone measurements. COARE output of air-sea fluxes are compared using either Saildrone-measured scalar wind including gustiness or the Saildrone vector mean wind including parameterized gustiness. Results are compared to quantify the impact of measured vs. parameterized wind variance on heat and momentum fluxes at the air-sea interface. Furthermore, we test for correlation between the measured minus parameterized gustiness to meteorological and oceanographic variables to explore possible corrections to the traditional COARE gustiness parameterization.