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Background to the ECMWF ERA-40 Re-Analysis project


The objectives of the European Centre for Medium-Range Weather Forecasts ERA-40 project are to produce and promote use of a comprehensive set of global analyses describing the state of the atmosphere, land and ocean-wave conditions from mid-1957 to August 2002. The ERA-40 project applies a modern Variational Data Assimilation technique (used in daily operational numerical forecasting at ECMWF) to the past conventional and satellite observations.

Production Streams

The data is being produced in three streams, defined by the availability of observational data for each given period:

Partner Organisations

A number of partner organisations are also involved to assess the quality of the global analyses, they are: In partnership with NCAR and NCEP (National Centers for Environmental Prediction, USA), the ECMWF has obtained a comprehensive archive of past observations to supplement its original observational archives running from 1979 to the present day. A Sea Surface Temperature/Ice dataset produced by the Hadley Centre and NOAA/NESDIS has been made available to the project through PCMDI (Program of Climate Model Diagnosis and Intercomparison, USA), which is also participating in the quality assessment of the products.

Improvements on ERA-15

ERA-15, the predecessor of ERA-40, covered the period January 1979 - February 1994 and used an earlier Optimum Interpolation analysis technique. The products are currently used in wide range of applications. A significant difference between ERA-40 and ERA-15 is in the use of satellite data. ERA-40 is using the TOVS radiances directly, while in ERA-15 temperature and humidity retrievals were used. In addition SSM/I Special and ERS data are used in ERA-40. The vertical resolution of the assimilating forecast model has been extended to 60 levels, with the top level at about 64 km. The model physics and the surface parametrization have been upgraded and improved since ERA-15 and ozone has been introduced as a model variable.

Explanation of Acronyms used on this page

ATOVS - Advanced Tiros Operational Vertical Sounder.
CMW - Cloud Motion Winds.
ERS - European Remote Sensing Satellite.
NESDIS - National Environmental Satellite, Data, and Information Service.
NOAA - National Oceanic and Atmospheric Administration (USA).
SSM/I - Sensor Microwave Imager.
TOVS - Tiros Operational Vertical Sounder.
VTPR - Vertical Temperature Profile Radiometer.