Estimation of the Analysis Error Variance of the 500 mb Height Analyses in the Northern Hemisphere, 1946–79

Abstract

The yearly variances of the analysis error of the 500 mb height north of 20°N are estimated from analyses covering the period 1946?79. A new method is presented. The error variances are computed directly from the analyses without any assumptions concerning the observational network, the observation error or the analysis system. The results show a general decrease of the analysis error variance up to 1970, since when it has been fairly constant. A weak increase is visible in analyses from 1976 onward. The present day error variance is about half of that for the years preceding the International Geophysical Year. Sudden peaks occur when the analysis center was changed. Local developments are discussed. When subsamples are compared with each other, the problematic area in 1955?62 turn out to be around the North Pole, around the Great Lakes, and the area westward from Kamchatka. Over these area some phenomena have been analyzed less accurately than expected. In 1962?70 a problematic area is found over the northern Atlantic.