Intercomparison of the NCEP/NCAR and the NASA/DAO Reanalyses (1985-1993)

In response to the climate community's need for long, consistent atmospheric datasets, the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) are producing a multiyear reanalysis dataset with a fixed assimilation system. Current plans call for the reanalysis to extend for at least 40 years (1957-current). Documentation of the reanalysis dataset and the assimilation system used to produce it is found in Kalnay et al. (1996). This reanalysis provides a valuable product for the research community because it is produced with a state-of-the-art fixed assimilation system and a large input database. The output, which is global and gridded, includes all prognostic fields and a large number of diagnostic quantities, all of which are provided four times daily. All reanalysis products will be available to the research community.

The purpose of this atlas is to provide an early look at the quality of the NCEP/NCAR and the NASA/Data Assimilation Office (DAO) reanalyses for a common period (1985-1993). Intercomparisons and comparisons to earlier operational analyses and to in situ and satellite observations are used to establish the level of uncertainty in various parameters. The main results are shown in terms of mean seasonal values and standard deviations with respect to season. Because the NCEP/NCAR assimilation system is frozen, many of the biases identified here are likely to persist in other years that have yet to be reanalyzed. Thus, this document should provide users of the data with a measure of how much confidence to place in various fields and, in particular, will serve to alert users about potential limitations of these datasets.