Random Analysis Error of 500 mb Height Analyses for the FGGE Year

Abstract

Different methods of studying the random error variance of 500 mb geopotential height analyses are discussed and applied. It has not been possible to show that the random errors of the operational analyses during the FGGE year have been smaller than those of previous years. In contrast to this, however, it is concluded that there have never been analyses of a quality comparable with the delayed-mode FOGE analyses (leaves IIIb/ECMWF). This conclusion is based on the whiteness of the error spectrum and the small variance of the random error. The variances of the random errors of the operational analyses over a dense observational network are small. The maxima are found over the Pacific, the Atlantic, the Himalayas and around the North Pole. Their intensity varies from one analysis set to another. In the delayed-mode analyses, the distribution of the error variance is flat. One operational analysis set shows a similar flat distribution. The reason for this flatness is believed to lie in the smoothing applied by the analysing center. A study of the smoothing is thus necessary in order to draw final conclusions.