MPI für Meteorologie / Atmosphere in the Earth System |
|The ERA-40 re-analysis|
|Authors:||Uppala, S. M.; Kallberg, P. W.; Simmons, A. J.; Andrae, U.; Bechtold, V. D.; Fiorino, M.; Gibson, J. K.; Haseler, J.; Hernandez, A.; Kelly, G. A.; Li, X.; Onogi, K.; Saarinen, S.; Sokka, N.; Allan, R. P.; Andersson, E.; Arpe, K.; Balmaseda, M. A.; Beljaars, A. C. M.; Van De Berg, L.; Bidlot, J.; Bormann, N.; Caires, S.; Chevallier, F.; Dethof, A.; Dragosavac, M.; Fisher, M.; Fuentes, M.; Hagemann, S.; Holm, E.; Hoskins, B. J.; Isaksen, L.; Janssen, P. A. E. M.; Jenne, R.; McNally, A. P.; Mahfouf, J. F.; Morcrette, J. J.; Rayner, N. A.; Saunders, R. W.; Simon, P.; Sterl, A.; Trenberth, K. E.; Untch, A.; Vasiljevic, D.; Viterbo, P.; Woollen, J.|
|Date of Publication (YYYY-MM-DD):||2005-10|
|Title of Journal:||Quarterly Journal of the Royal Meteorological Society|
|Journal Abbrev.:||Q. J. R. Meteorol. Soc.|
|Issue / Number:||612|
|Abstract / Description:||ERA-40 is a re-analysis of meteorological observations from September 1957 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many institutions. The observing system changed considerably over this re-analysis period, with assimilable data provided by a succession of satellite-borne instruments from the 1970s onwards, supplemented by increasing numbers of observations from aircraft, ocean-buoys and other surface platforms, but with a declining number of radiosonde ascents since the late 1980s. The observations used in ERA-40 were accumulated from many sources. The first part of this paper describes the data acquisition and the principal changes in data type and coverage over the period. It also describes the data assimilation system used for ERA-40. This benefited from many of the changes introduced into operational forecasting since the mid-1990s, when the systems used for the 15-year ECMWF re-analysis (ERA-15) and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis were implemented. Several of the improvements are discussed. General aspects of the production of the analyses are also summarized.
A number of results indicative of the overall performance of the data assimilation system, and implicitly of the observing system, are presented and discussed. The comparison of background (short-range) forecasts and analyses with observations, the consistency of the global mass budget, the magnitude of differences between analysis and background fields and the accuracy of medium-range forecasts run from the ERA-40 analyses are illustrated. Several results demonstrate the marked improvement that was made to the observing system for the southern hemisphere in the 1970s, particularly towards the end of the decade. In contrast, the synoptic quality of the analysis for the northern hemisphere is sufficient to provide forecasts that remain skilful well into the medium range for all years. Two particular problems are also examined: excessive precipitation over tropical oceans and a too strong Brewer–Dobson circulation, both of which are pronounced in later years. Several other aspects of the quality of the re-analyses revealed by monitoring and validation studies are summarized. Expectations that the 'second-generation' ERA-40 re-analysis would provide products that are better than those from the first-generation ERA-15 and NCEP/NCAR re-analyses are found to have been met in most cases.
|Free Keywords:||data assimilation; numerical weather prediction; observing system|
|External Publication Status:||published|
|Communicated by:||Carola Kauhs|
|Affiliations:||MPI für Meteorologie|
|External Affiliations:||European Ctr Medium Range Weather Forecasts, Reading RG2 9AX, Berks, England.; Lawrence Livermore Natl Lab, Program Climate Model Diagnosis & Intercomparison, Livermore, CA USA.; Chinese Acad Sci, Inst Atmospher Phys, Beijing, Peoples R China.; Japan Meteorol Agcy, Tokyo, Japan.; Univ Reading, Environm Syst Sci Ctr, Reading RG6 2AH, Berks, England.; European Org Exploitat Meteorol Satellites, Darmstadt, Germany.; Koninklijk Nederlands Meteorol Inst, De Bilt, Netherlands.; Univ Reading, Dept Meteorol, Reading RG6 2AH, Berks, England.; Natl Ctr Atmospher Res, Boulder, CO 80307 USA.; Meteorol Off, Exeter, Devon, England.; Meteo France, Toulouse, France.; NOAA, NWS, Natl Ctr Environm Predict, Washington, DC 20230 USA.|
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