Spatial Correlation of the 24-Hour ECMWF Forecast Error

Abstract

The spatial autocorrelation of the error of the ECMWF 24-h forecast of 500 mb geopotential height during 1980?83, hereafter referred to as the ?forecast error,? is studied. The leading EOF of the forecast error describes a ?teleconnection? between the Himalayas and the Pacific/European sector. The third EOF resembles the analysis error. Approximations for the isotropic part of the autocorrelation are presented. They consist of two source terms having different spatial scales. A ?random-like? term could be due to model errors in baroclinic processes or to random analysis errors. A ?scale-dependent? term could be due to model errors in barotropic processes and over mountain areas, or to analysis errors over data-sparse areas or mountains. The terms do not contribute uniformly. The ?scale-dependent? term is strongest over mountains The relative contribution of that term decreased from forecasts of 1980?81 to those of 1982?83.