ECMWF ERA-40 - European Reanalysis

Topics

• Access
• Description
• Parameters
• Coverage, spatial and temporal resolution
• Data quality
• Contact person
• References
• Data citation and License

Access

RESTRICTED:

• Get ERA Interim data at ECMWF for registered ECMWF users

RESTRICTED: This link to the data set is only available for a restricted user group.  The data set is only accessible in CEN/MPI net or accessible from external nets with a customer account.  Please contact ICDC if you would like to access this data from outside the network.

• Data access via file system:  /data/icdc/reanalyses/era_40/

to top

Description

The reanalysis data set ERA-40 is the predecessor of ERA-Interim and ERA-5. ICDC offers a subset of the data for internal use.

Already in 1995 the ECMWF in Reading presented the Reanalysis project ERA-15 (Gibson and others, 1997) for the period 01/12/1978 12:00 02/28/1994 18:00 H. Due to the enhancements of the forecast system and the data assimilation, the more extensive reanalysis project ERA-40 (Simmons and Gibson, 2000; Uppala and others, 2005) was presented in 2003. ERA-40 covers the period 9.1.1957 to 31.8.2002 0:00 UTC 18:00 UTC, and begins with the International Geophysical Year 1958, which provided many observations.

The three-dimensional ERA-40 data set was created consistently with one version of the Integrated Forecasting System (IFS) of the ECMWF. The model results are based on not only the routine measurements, but also included all available and appropriate observational data. This assimilated observational data are from diverse sources, such as weather stations, radio soundings, ship measurements and since the 1970s also satellite measurements.

The assimilation model used has a horizontal spectral resolution of T159 and L60 height level. The spatial resolution of T159 corresponds to a spatial resolution of 1.125 ° x 1.125 ° in the geographical grid. The data are 6-hourly (6H) at four dates (0:00, 6:00, 12:00, 18:00 UTC) or monthly averaged (MM), on model levels (ML), pressure levels (PL ) or as a base value (SFC), analysis (0h) or prediction (6h). These shortcuts can also be found in the file name in the CERA database.

The data set contains all the important atmospheric parameters. It was build for a time period of 45 years with the same model to be consistent. The model completes the spatial and temporal gaps in the observations. But this means , especially in areas with traditionally few available measurements such as the Arctic, a loss of quality in the modeled data.

Last update of data set at ICDC: 2011

to top

Parameters

Parameters of the ERA-40 data set: List of at ICDC available parameters, see ECMWF for complete list.

Name and Abbreviation	Unit	Variable Number	Level
Geopotential, z	m2 s-2	129	100000, 92500, 85000, 77500, 70000, 60000, 50000, 40000, 30000, 25000, 20000, 15000, 10000, 7000, 5000, 3000, 2000, 1000, 700, 500, 300, 200, 100
Vertical velocity "OMEGA", w	Pa s-1	135	100000, 92500, 85000, 77500, 70000, 60000, 50000, 40000, 30000, 25000, 20000, 15000, 10000, 7000, 5000, 3000, 2000, 1000, 700, 500, 300, 200, 100
Temperature, t	K	130	100000, 92500, 85000, 77500, 70000, 60000, 50000, 40000, 30000, 25000, 20000, 15000, 10000, 7000, 5000, 3000, 2000, 1000, 700, 500, 300, 200, 100
U component of wind, u	m/s	131	100000, 92500, 85000, 77500, 70000, 60000, 50000, 40000, 30000, 25000, 20000, 15000, 10000, 7000, 5000, 3000, 2000, 1000, 700, 500, 300, 200, 100
V component of wind	m/s	132	100000, 92500, 85000, 77500, 70000, 60000, 50000, 40000, 30000, 25000,  20000, 15000, 10000, 7000, 5000, 3000, 2000, 1000, 700, 500, 300, 200, 100

to top

Coverage, spatial and temporal resolution

Period and temporal resolution:

• 1957/09/01 0:00 UTC to 2002/08/31 18:00 UTC
• 6-hourly and monthly

Coverage and spatial resolution:

• Global
• Spatial resolution: about 1.125° x 1.125°, T159 Gaussian grid
• Geographic longitude: 0.0°E to 358.875°E
• Geographic latitude: -89.1415°N to 89.1415°N
• Dimension: 320 columns x 160 rows
• Altitudes: 23 Pressure levels

Format:

• NetCDF (one parameter: 75 Gbyte)

to top

Data quality

See the ECMWF Report "Data usage and quality control for ERA-40, ERA-Interim and the operational ECMWF data assimilation system" in references.

Some studies have a critical view on the quality of ERA40. Here are some examples:

• Trenberth and others (2001) address the quality of reanalyses in the tropics.
• Bengtsson et al (2004a) analysis if it is possible to calculate climate trends from reanalysis data. The question rises due to changes in type and number of observational data that could lead to trends and artefacts in the reanalysis, especially due to assimilation of satellite data in the middle of the time series.
• Bengtsson et al (2004b) compare reanalysis data to observational data and find out that reanalysis data can only with reservations be used for long term climate trend analysis due to the inhomogeneities in time of the observational data.
• Bengtsson et al (2004c) have analysed the quality of the water cycle (precipitation, evaporation).
• Erroneous precipitation data are described in some studies, e.g. Upalla et al (2005) describe problems in the tropics.
• It is not possible to represent the real orography in the model on which ERA40 is based (see ECMWF website Model Orography)
• Unrealistic trends in sea ice were found by Bromwich et al (2004)

to top

Contact

Annika Jahnke-Bornemann

ICDC / CEN / University of Hamburg
E-Mail: annika.jahnke-bornemann"AT"uni-hamburg.de

At ECMWF:

Name: Sakari Uppala
Institute: European Centre for Medium-Range Weather Forecasts (ECMWF)
Address: Shinfield Park, Reading, RG2 9AX, GB

to top

References

Literature:

• ECMWF Report "Data usage and quality control for ERA-40, ERA-Interim and the operational ECMWF data assimilation system", 2011 (pdf, not barrier free)
• [Bengtsson et al 2004a] Bengtsson, L., Hagemann, S., and Hodges, K. I. (2004), Can climate trends be calculated from reanalysis data? J. Geophys. Res., 109, D11111, doi:10.1029/2004JD004536. https://doi.org/10.1029/2004JD004536
• [Bengtsson et al 2004b] L. Bengtsson, K.I. Hodges & S. Hagemann (2004) Sensitivity of the ERA40 reanalysis to the observing system: determination of the global atmospheric circulation from reduced observations, Tellus A: Dynamic Meteorology and Oceanography, 56:5, 456-471, DOI: 10.3402/tellusa.v56i5.14466. https://doi.org/10.3402/tellusa.v56i5.14466 
• [Bengtsson et al 2004c] L. Bengtsson, K.I. Hodges & S. Hagemann (2004) Sensitivity of large-scale atmospheric analyses to humidity observations and its impact on the global water cycle and tropical and extratropical weather systems in ERA40, Tellus A: Dynamic Meteorology and Oceanography, 56:3, 202-217, DOI: 10.3402/tellusa.v56i3.14412. https://doi.org/10.3402/tellusa.v56i3.14412
• [Bromwich et al 2004] Bromwich, D. H., & Fogt, R. L. (2004). Strong Trends in the Skill of the ERA-40 and NCEP–NCAR Reanalyses in the High and Midlatitudes of the Southern Hemisphere, 1958–2001, Journal of Climate, 17(23), 4603-4619. https://doi.org/10.1175/3241.1  
• [Gibson et al 1997] GIBSON, J.K. ; KÅLLBERG, P. ; UPPALA, S. ; NOMURA, A.; HERNANDEZ, A. ; SERRANO, E.: ERA Description. In: ECMWF ERA-15 Project Report Series (1997), Nr. 1. – ECMWF, https://www.ecmwf.int/sites/default/files/elibrary/1997/9584-era-description.pdf  (pdf, not barrier free)
• [Simmons u. Gibson 2000] SIMMONS, A. J. ; GIBSON, J. K.: The ERA-40 Project Plan. In: The ERA-40 Project Report Series (2000), Nr. 1. https://www.ecmwf.int/sites/default/files/elibrary/2000/12272-era-40-project-plan.pdf (pdf, not barrier free)
• [Trenberth et al 2001] Trenberth, K. E., Stepaniak, D. P., Hurrell, J. W., & Fiorino, M. (2001). Quality of Reanalyses in the Tropics, Journal of Climate, 14(7), 1499-1510. https://doi.org/10.1175/1520-0442(2001)014<1499:QORITT>2.0.CO;2
• [Uppala et al 2005] Uppala, S.M., KÅllberg, P.W., Simmons, A.J., Andrae, U., Bechtold, V.D.C., Fiorino, M., Gibson, J.K., Haseler, J., Hernandez, A., Kelly, G.A., Li, X., Onogi, K., Saarinen, S., Sokka, N., Allan, R.P., Andersson, E., Arpe, K., Balmaseda, M.A., Beljaars, A.C.M., Berg, L.V.D., Bidlot, J., Bormann, N., Caires, S., Chevallier, F., Dethof, A., Dragosavac, M., Fisher, M., Fuentes, M., Hagemann, S., Hólm, E., Hoskins, B.J., Isaksen, L., Janssen, P.A.E.M., Jenne, R., Mcnally, A.P., Mahfouf, J.‐F., Morcrette, J.‐J., Rayner, N.A., Saunders, R.W., Simon, P., Sterl, A., Trenberth, K.E., Untch, A., Vasiljevic, D., Viterbo, P. and Woollen, J. (2005), The ERA‐40 re‐analysis. Q.J.R. Meteorol. Soc., 131: 2961-3012. https://doi.org/10.1256/qj.04.176 

Websites:

• ECMWF Parameter Table 128, https://apps.ecmwf.int/codes/grib/param-db?&filter=grib1&table=128 
• ECMWF Reanalysis - 40 years (ERA-40), https://www.ecmwf.int/en/forecasts/dataset/ecmwf-reanalysis-40-years
• ERA-40 Atlas, https://sites.ecmwf.int/era/40-atlas/docs/index.html  
• ECMWF Model Orography, https://confluence.ecmwf.int/display/FUG/Model+Orography 

to top

Data citation, License, and Acknowledgments

Please cite the data as follows:

Uppala et al., 2005: The ERA-40 re-analysis. In: Quarterly Journal of the Royal Meteorological Society 131 (2005), 2961-3012. doi:10.1256/qj.04.176.

and with the following acknowledgments:

Thanks to ICDC, CEN, University of Hamburg for data support.

License

You can find license information on the ECMWF project page.

to top