Air-sea stability effects on the 10 m winds over the global ocean: Evaluations of air-sea flux algorithms

Abstract

Spatial and temporal variability of the impact of air-sea stratification on the differences between satellite-derived 10 m equivalent neutral wind speeds and stability-dependent (e.g., in situ) 10 m wind speeds are quantitatively examined over the global ocean. The influences of stability are compared with three air-sea flux algorithms, Coupled Ocean-Atmosphere Response Experiment (version 3.0), Bourassa-Vincent-Wood, and Liu-Katsaros-Businger. Analyses are first presented at many individual buoy locations and then are extended to the global ocean with the use of rain-free wind measurements from the SeaWinds scatterometer on the QuikSCAT satellite, gridded at a resolution of 0.25° × 0.25°. Overall, stability-dependent winds are found to be weaker than equivalent neutral winds by 0.2 m s-1 on the basis of 7619 monthly mean values from 208 buoys during 2000-2005. Differences based on hourly winds can be as large as ±0.5 m s-1. Results remain robust regardless of which air-sea flux algorithm is used. Monthly rain-free gridded QuikSCAT measurements, combined with atmospheric stability determined using near-surface variables from the European Centre for Medium-Range Weather Forecasts 40-year reanalysis, demonstrate the effects of stratification on the 10 m winds globally. Differences in stability-dependent and neutral winds are substantially nonsymmetrical and reveal locations where the former is stronger than the latter. These differences may cause physically significant biases in air-sea fluxes if they are not properly considered, especially near the Kuroshio and Gulf Stream current systems. Copyright 2008 by the American Geophysical Union.