Covariance Analyses of Satellite-Derived Mesoscale Wind Fields

Abstract

Statistical structure functions have been computed independently for nine satellite-derived, mesoscale wind fields that were obtained on two different days. Small cumulus clouds were tracked at 5 min intervals, but since these clouds occurred primarily in the warm sectors of midlatitude cyclones the results cannot be considered representative of the circulations within cyclones in general. The field structure varied considerably with time and was especially affected if mesoseale features were observed. The wind fields on the 2 days studied were highly anisotropic with large gradients in structure occurring approximately normal to the mean flow. Structure function calculations for the combined set of satellite winds were used to estimate random error present in the fields. It is concluded for these data that the random error in vector winds derived from cumulus cloud tracking using high-frequency satellite data is less than 1.75 m s-1. Spatial correlation functions were also computed for the nine data sets. Normalized correlation functions were considerably differeni for u and v components and decreased rapidly as data point separationincreased for both components. The correlation functions for transverse and longitudinal components decreased less rapidly as data point separation increased.