A comparison of operational global analyses from the European Centre for Medium Range Weather Forecasts (ECMWF) and the National Meteorological Center (NMC)

Abstract

A comparison of the analyses from the ECMWF/WMO Global Analysis Dataset produced by the European Centre for Medium Range Weather Forecasts (ECMWF) and the operational analyses of the National Meteorological Center (NMC) is made for an average of five Januaries and five Julys during the period 1980–1984 to assess the utility of these datasets for climate and other studies. The time and zonal mean, the square root of the zonally averaged standing eddy variance and the square root of the zonally averaged transient eddy variance are computed for the differences in the analyses of the horizontal wind components, temperature, geopotential, and specific humidity. A “reliability” measure which compares the variance of the differences to observed variances is used to assess the datasets. The results indicate that monthly means and daily analyses of the five variables are not reliable in the tropics nor in the south polar regions. In general, reliable monthly means and daily analyses are found in the mid-latitudes of the Southern Hemisphere and in the extra-tropical Northern Hemisphere, with the exception of the daily analyses of specific humidity which are reliable only in the extra-tropics of the Northern Hemisphere during January.