Background to the ECMWF ERA-40 Re-Analysis project
The objectives of the European Centre for Medium-Range Weather Forecasts
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
The data is being produced in three streams, defined by the availability of
observational data for each given period:
- Stream 1 (1987-2002): Assimilating the latest observation types
ATOVS and CMW).
- Stream 2 (1957-1972): Pre-satellite, old observation types only.
- Stream 3 (1972-1988): Assimilating some satellite observation types
(VTPR, TOVS and CMW).
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.
- the Hadley Centre for Climate Prediction and Research, UK.
- the Koninklijk Nederlands Meteorologisch Instituut.
- Météo France, Centre National de Récherches Météorologiques.
- Max Plank Institut für Meteorologie, Germany.
- University of Reading, Department of Meteorology, UK
- the National Center for Atmospheric Research (NCAR), USA.
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.