The first ECMWF Re-Analysis (ERA-15) project was devised in response to the wishes expressed by many users of data from the ECMWF archives. The goal of the project was to develop a global atmospheric data assimilation system to analyze in an internally consistent way the record of atmospheric data (from the earth's surface to 10 hPa) for the period 1979-1993, and then to produce a validated and documented 15-year data set of assimilated data at high horizontal and vertical resolution. This project was successfully completed in 1996, and the results, together with reanalyses from NCEP and NASA have proved a catalyst for much investigative research.
The ERA-40 project is designed to enable a 40 year reanalysis, from 1958 to 1997 or later, to take advantage of both the advances made over recent years in data assimilation, and of the extensive data rehabilitation performed by NCAR. It will provide a useful comparative and complimentary data set to that generated by the NCEP reanalysis.
ERA-40 will employ a 3-dimensional variational data assimilation scheme using a 50-level forecast model and coupling with wave model. Extensive pre-production efforts are being made to address deficiencies which were noted from the previous 15-year re-analysis (ERA-15). Substantial progress in this area has been made, and it is expected that ERA-40 analyses will be of significantly higher quality than those of ERA-15, given sufficient data coverage.
Attempts will be made to maximise the use of all available forms of data, especially the satellite data available over more recent years. Reanalysis will be performed both with and without these major new data types to enable their impact to be diagnosed and assessed.
The resulting data set will provide global three dimensional descriptions of the velocity, temperature, geopotential and humidity fields for the atmosphere. In addition, analyses of surface parameters (temperature, pressure, soil moisture, etc.), surface fluxes of heat, moisture, radiation and other diagnosed quantities will be included. A full extraction service for the data set will be supported.
This paper will describe the planning of the project, the results to be produced, and the progress made to date.
The ECMWF re-analysis effort receives support in various forms from the ECMWF Council and Member States, the University of California (PCMDI), the Japan Meteorological Agency, MPI, NCAR, NCEP, NSIDC, BoM Melbourne, and many individual scientists who have proffered useful advice