Saildrone Direct Covariance Wind Stress in Various Wind and Current Regimes of the Tropical Pacific

Abstract

High frequency wind measurements from Saildrone autonomous surface vehicles are used to calculate wind stress in the tropical East Pacific. Comparison between direct covariance (DC) and bulk wind stress estimates demonstrates very good agreement. Building on previouswork that showed the bulk input data was reliable, our results lend credibility to the DC estimates. Wind flow distortion by Saildrones is comparable to or smaller than other platforms. Motion correction results in realistic wind spectra, albeit with signatures of swell-coherent wind fluctuations that may be unrealistically strong. Fractional differences between DC and bulk wind stress magnitude are largest at wind speeds below 4 m s−1. The size of this effect, however, depends on choice of stress direction assumptions. Past work has shown the importance of using current-relative (instead of Earth-relative) winds to achieve accurate wind stress magnitude. We show that it is also important for wind stress direction.

The Importance of Contemporaneous Wind and pCO2 Measurements for Regional Air‐Sea CO2 Flux Estimates

“…A recent study investigated the flow distortion of Saildrone in various wind-wave conditions and found that it is comparable to or less than that on ships and buoys (Reeves Eyre et al, 2023). Due to the position of the sonic anemometer at the forward edge of the Saildrone wing, it is thought that flow distortion is minimized (Gentemann et al, 2020).…”

Atmospheric Fronts Shaping the (Sub)Mesoscale SST‐Wind Coupling Over the Southern Ocean: Observational Case

“…In recent years, Saildrone (Uncrewed Surface Vehicle, Figure 1a) exhibits the potential to conduct measurements of the upper ocean and lower atmosphere layer in severe conditions (D. Zhang et al., 2019; Vazquez‐Cuervo et al., 2019; Gentemann et al., 2020; Nagano & Ando, 2020; Sutton et al., 2020; Reeves Eyre et al., 2023). These new features recorded by Saildrone can improve our understanding of fine‐scale air‐sea interaction and refine the parameterization in numerical weather models.…”