Revised interpolation statistics for the Canadian data assimilation procedure: their derivation and application

Abstract

The first part of this paper presents the results of a study of the structure of the observed residuals, or differences, between radiosonde data and the short-range forecasts that are used as trial fields in an operational hemispheric data assimilation scheme. The study is based on fitting appropriate functional representations to horizontal correlations of observed height and wind residuals. We use a representation for the height residuals consisting of a sum of two degenerate third-order auto-regressive functions of the form (1 + cr + c2r2/3) exp (-cr), where r represents radial distance. For the wind residuals, we use the functional form that follows by geostrophy. We also present other statistics relating to the performance of the data assimilation procedure, such as vertical profiles of the magnitude of the observed wind and height residuals for various regions. In the second part of the paper, the results of the study are used as a basis for specifying interpolation statistics for the objective analysis. -from Authors