On the Accuracy of 500 mb Analysis with Special Reference to Numerical Forecasting

The result of an analysis experiment is discussed. From 29 different analyses of one and the same 500 mb chart certain parameters were calculated. The standard deviation of the height of the 500 mb surface had an average value of 15 gdm, determined over an area of 4,200 times 8,100 km. The correlation coefficient between the observed changes and the changes forecast with a numerical barotropic forecast varied between 0.53 and 0.77 (24h.), 0.77 and 0.84 (48h), respectively. Some other verification parameters are given. Calculations of the geostrophic wind are carried through for all analyses, both at points, over areas and along certain tracks. The deviations due to the differences in analysis are sometimes considerable.