Structure and Simulation of the Random Analysis Error of 500 mb Geopotential Heights

Abstract

The structure of the analysis error field of the 500 mb height north of 20°N was estimated from the differences between analyses issued by two different centers. The resulting variance field is very similar to that computed with the aid of the optimum interpolation. The leading empirical orthogonal functions of the analysis error show large cells over areas with a sparse observational network. Artificial analysis error fields are constructed with the aid of empirical orthogonal functions. The structure of these fields is the same as that derived from the analyses. The model results indicate that the perturbation fields can be produced without correlating them with previous analyses or forecasts. The smoothing of the analyses contributes rather much to the forecasting error and should therefore be simulated. The model results, however, are valid only if the forecasting error can be measured with the root-mean-square error.