The ERA‐40 re‐analysis

Abstract

SUMMARY 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 * Corresponding author: European Centre for Medium-Range Weather Forecasts, Shinfield Park, Reading RG2 9AX, UK. e-mail: adrian.simmons@ecmwf. 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 firstgeneration ERA-15 and NCEP/NCAR re-analyses are found to have been met in most cases.

Assessing Bias and Uncertainty in the HadAT-Adjusted Radiosonde Climate Record

“…This is applied to time series of seasonal mean differences between station data and weighted composites of data from neighboring stations. The weighting of each contributing neighbor station is equal to the correlation coefficient between seasonal mean anomalies from reanalysis fields [National Centers for Environmental PredictionNational Center for Atmsopheric Research (NCEP-NCAR; Kalnay et al 1996) or the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40; Uppala et al 2005)] sampled at station locations over the period . Neighbors are selected only from locations that fall within a contiguous area with correlation coefficients greater than 1/e surrounding the target station.…”

Absorbing Aerosols and Summer Monsoon Evolution over South Asia: An Observational Portrayal

“…Atmospheric and surface variables are derived from the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA-40) (Uppala et al 2005) monthly data on a 2.5°ϫ 2.5°grid and at 23 vertical isobaric levels and were obtained from the National Center for Atmospheric Research (NCAR). ERA-40 was produced by running the spectral model at T159 (roughly 125 km) horizontal resolution (and with 60 vertical hybrid levels).…”

Impact of climate indicators on continental‐scale potential groundwater recharge in Africa

“…For the 1960-1978 period, boundary forcings were prescribed by the ERA40 re-analysis data (Uppala et al, 2005). The associated climate data are publicly available at http://www.ecmwf.int/en/forecasts/datasets/era- 40-dataset-sep-1957-aug-2002.…”