Diagnosis of the ECMWF's Re-analysis

Paul Berrisford, Alan O'Neill and Brian Hoskins

Centre for Global Atmospheric Modelling
Department of Meteorology
University of Reading

The Centre for Global Atmospheric Modelling (CGAM) has helped make a portion of the European Centre for Medium-Range Weather Forecasts (ECMWF) re-analysis (ERA) available to the U.K academic community. Operational analysis systems of the various weather prediction centre's around the world are continually changing in order to try and improve forecast skill. Unfortunately, this introduces spurious temporal variability into the data. Re-analysis is an analysis of past meteorological observations with a modern and unchanging analysis system. The resulting four-dimensional global atmospheric dataset is the best possible representation of the structure and evolution of the earth's atmosphere that can be made today by any particular forecasting centre. The ERA dataset covers the period from January 1979 through to February 1994.

Evapouration - Precipitation for the years 1979 to 1993. Shows high rainfall along the equator and excess evapouration to the north and south of the equator.


The bulk of the data has a temporal resolution of 6-hours. Data are represented both in spectral (at a resolution of T106) and grid point (on a so called N80 reduced Gaussian grid) form on 31 hybrid model levels. The latter follow the terrain near the ground and change smoothly to pressure levels by the mid-stratosphere. Data are also available on 17 standard pressure levels in spectral form. A limited number of daily forecast 24-hour accumulations are also available. These comprise surface fields such as precipitation, long and short wave radiation and fluxes of sensible and latent heat. These data are available in GRIB format and are archived at the British Atmospheric Data Centre (BADC).

CGAM has also computed various time mean and time series diagnostics from the ECMWF re-analysis dataset. Time mean data are available at the ground, on pressure and isentropic levels and several levels thought to lie in the vicinity of the tropopause. Time averages were computed for each month of the ERA period. Monthly climatologies were computed for each of the 12 months of the year from the 15 months available in the ERA period 1979-1993. The four seasonal climatologies were then computed from the monthly climatologies. Daily (12GMT) time series diagnostics are available on 17 pressure and 17 isentropic levels. This data is available in DRS format and is archived at the BADC.


Skin reservoir content for the years 1979 to 1993. Shows desert and water rich land areas.

Furthermore, CGAM has made available to the BADC the operational analyses for the post ERA period i.e. from March 1994 to the present day. CGAM keeps the dataset up to date on a monthly basis so that a continuous dataset with 6-hourly temporal resolution is available from January 1979 through to the present.