A Simple Model for the Skewness of Global Sea Surface Winds

Abstract

A strong linear relationship between the mean and skewness of global sea surface winds (both zonal and meridional) is shown to exist, such that where the wind component is on average positive, it is negatively skewed (and vice versa). This relationship is observed in reanalysis, satellite, and buoy data. This relationship between the mean and skewness fields of sea surface winds follows from the nonlinear surface drag predicted for a turbulent boundary layer by Monin?Obukhov similarity theory since forcing perturbations speeding the wind up are subject to a stronger drag force than perturbations slowing it down. Furthermore, it is demonstrated that the results of an empirical fit of observed surface winds to a stochastic differential equation presented in a recent study by Sura are consistent with the white-noise limit of the momentum equations for a turbulent boundary layer subject to fluctuating forcing, albeit with a somewhat different physical interpretation.