BOX 4-2

NCEP-NCAR Global Atmospheric Reanalysis: An Example of the Benefits of Data Stewardship

The National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) Reanalysis provides a standardized time series of the evolution of the global atmosphere starting in 1948 (Kalnay et al., 1996). This suite of data products, which was made possible by scientific community foresight and resources from an operational numerical weather prediction center, has proven to be an extremely valuable resource for a broad range of scientific studies, and in many respects it serves as a model for effective stewardship practices.

More than 40 year ago, long before data stewardship became part of the data management vocabulary, Roy Jenne, then at NCAR, and other like-minded data managers and providers at NOAA and NASA began sharing, collecting, documenting, and preserving a wide variety of in situ and satellite observations of atmospheric conditions. These data and metadata preservation activities established long-term collections that ultimately became a major input data component for the data assimilation and forecast processes used to create the NCEP–NCAR Reanalysis. In fact, it would be fair to say that reanalysis would not have been possible over the nearly 60-year period of record or at the fidelity we have come to expect today without the activities of Jenne and his colleagues.

Stewardship is much more than data preservation. A typical dataset used in the NCEP-NCAR Reanalysis has gone through several phases of preparation, usage, and improvement, and careful stewardship is required during each of these phases. For example, through user studies that analyze the data for scientific content and complimentary examinations and quality control by data stewards, fixable problems and systematic errors are occasionally uncovered. Data stewards are critical during this stage because they work with scientists to fully define the problem and to design processes to fix the data. After the data are improved, the metadata are updated and user access is refreshed with a new version of the data set. In this way historical data sets improve in quality through a stewardship-supported life cycle (see Figure 4-1). Many data sets used in the NCEP-NCAR Reanalysis have experienced several such iterations, and this process has also benefited subsequent reanalyses, such as the European Center for Medium-range Weather Forecasts (ECMWF) ERA-40 data set. The importance of data stewardship for the success of these efforts has been documented, and community-based plans have been developed to make further improvements (Schubert et al., 2006).

Stewardship also supports the NCEP-NCAR Reanalysis (and other reanalyses) by providing data security, multiple access points for products, user consulting, and routine time series extension. NCEP does not archive the Reanalysis for public access; rather, it distributes copies to both NCAR and NCDC to ensure that the data are securely preserved. These two institutions also provide data support services and a variety of access methods to obtain the NCEP-NCAR Reanalysis. NOAA’s Earth Systems Research Laboratory (ESRL) provides additional support, such as transforming some of the most popular data to different formats so users can employ their favorite tools—for example, direct access by remote applications—to exploit the data. NCEP’s collaboration with these other groups results in extensive and well-supported data availability for thousands of users worldwide.

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