ECMWF ERA-40 upper air analyses monthly means

SOURCE: Data Support Section Dataset ds126.1

DATA DESCRIPTION: ECMWF ERA-40 High Resolution Upper Air Analyses: T85 resolution: 23 pressure levels containing monthly means.



GRID: T85 Gaussian (256 x 128)

TIMES: Monthly Means

DATES: September 1957 - August 2002

LEVELS: 23 pressure (hPa) levels: 1, 2, 3, 5, 7, 10, 20, 30, 50, 70, 100, 150, 200, 250, 300, 400, 500, 600, 700, 775, 850, 925, 1000

TIMES: Monthly means

CURRENT HOLDINGS: Jan 1957-Dec 2001


Description Name Units
Geopotential Z m2 s-2
Divergence DIV s-1
Ozone mass mixing ratio 03 kg kg-1
Potential Vorticity PV K m2 kg-1 s-1
Relative Humidity RHUM %
Specific Humidity Q kg kg-1
Temperature T K
U-component of wind U m s-1
V-component of wind V m s-1
Vertical pressure velocity OMEGA Pa s-1
Relative vorticity




Filenames: The MSS file names are based upon ECMWF style file names and are consistent with those suggested by the Data Support Section. Generic Name: where yyyy is the 4-digit year, and vName is the lower case of the netCDF variable name.

For example: would be the file containing the 12 monthly means for Temperature.

File size: Each file is 36.2MB/variable.


Uppala, S.M., P.W. Kallberg, A.J. Simmons, et al (2005): The ERA-40 Reanalysis. Q.J.R. Meteorol. Soc. 131, 612, 2961-3012.

Uppala, S., P. Kallberg, A. Hernandez, S. Saarinen, M. Fiorino, X. Li, K. Onogi, N. Sokka, U. Andrae, V. Da Costa Bechtold (2004): ERA-40: ECMWF 45-year reanalysis of the global atmosphere and surface conditions 1957-2002. ECMWF Newsletter No. 101 - Summer/Autumn 2004: 2-21.

ERA-40 Project Report Series

Climate Analysis Section references using ERA40 data. Often, these illustrate strengths and weaknesses of the ERA40 dataset.

netCDF metadata: CAVEAT: longitude coordinate variable

The netCDF files were derived from GRIB files containing the T85 resolution ERA-40 data. The GRIB format allows only three decimal places for the longitude increment. Since the T85 grid has a longitude spacing of 1.40625 degrees, the automatically generated longitudes which use the GRIB spacing are not correct. Users can readily generate the correct longitudes or can download the values from an ascii file.

HISTORY: This dataset is a netCDF version of ds126.1 which is archived in GRIB format. The original dataset was implemented and computed by NCAR's Data Support Section (DSS). It forms an essential part of efforts undertaken in late 2004, early 2005, to produce an archive of selected segments of ERA-40 on a standard transformation grid. In this case, ERA-40 monthly mean upper air variables on 23 pressure levels were transformed from either spherical harmonics (geopotential, temperature, vertical pressure velocity, vorticity, divergence, relative humidity), or a reduced N80 Gaussian grid (potential vorticity, specific humidity, ozone mass mixing ratio), to a 256x128 regular Gaussian grid at T85 spectral truncation. In addition, horizontal wind components were derived from spectral vorticity and divergence and also archived on a T85 Gaussian grid. All scalar fields were transformed using routines from the ECMWF EMOS library, whereas the horizontal winds were obtained using NCAR's Spherepack library. The choice of a T85 Gaussian grid was based on considerations of limiting the volume of new data generated to a moderate level, and to match the horizontal resolution of the Community Atmosphere Model (CAM) component of the Community Climate System Model (CCSM)

The netCDF version was produced by the Climate Analysis Section as a community service. The contents conform to the netCDF Climate and Forecast (CF) Metadata Convention . The purpose is to facilitate evaluation of the CCSM and to produce datasets that may be more readily analyzed by commonly available software tools.


The ERA-40 data are available for non-commercial use within the U.S. and at UCAR member institutions. All data are available from the NCAR Mass Storage System (MSS). Use of the data at NCAR does not require the submission of a permission form. However, if you do not have access to the MSS or wish to utilize the data outside of NCAR, then a permission form must be signed. Redistribution of this data under any circumstances is strictly prohibited.