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NCEP/NCAR Reanalysis 1: Spectral Coefficients

We have transitioned the data files from netCDF3 to netCDF4-classic format on Monday Oct 20th, 2014.

Note, spectral coefficients are being converted to integer*2 netCDF4-classic format and reatin their original packing (which is dependent on packing parameters as a function of level.

Other Grid Types: NCEP Reanalysis Main Page | Pressure Level Data | Surface Data | Surface Flux Data | Other Flux Data |Spectral Coefficents Data | Tropopause Data

Brief Description:

  • NCEP/NCAR Reanalysis 1:Spectral Coefficients from the global analysis model.

Temporal Coverage:

  • 4-times daily 1948/01/01 to present

Spatial Coverage:

  • T62 Spectral Coefficients


  • 28 Sigma levels: 0.995, 0.9821, 0.9644, 0.9425, 0.9159, 0.8838, 0.8458, 0.8014, 0.7508, 0.6943, 0.6329, 0.5681, 0.5017, 0.4357, 0.372, 0.3125, 0.2582, 0.2101, 0.1682, 0.1326, 0.1028, 0.0782, 0.058, 0.0418, 0.0288, 0.0183, 0.0101, 0.0027
  • Some variables not defined at all levels.

Update Schedule:

  • Daily

Note: These variables are instantaneous values at the reference time.

Variable Statistic Level Download File
Divergence 4-times Daily 28 levels /Datasets/ncep.reanalysis/spectral/div.spec.yyyy.nc
Orography 4-times Daily Surface /Datasets/ncep.reanalysis/spectral/oreg.spec.nc
Natural Log of Pressure 4-times Daily Surface /Datasets/ncep.reanalysis/spectral/pres.nlog.sfc.yyyy.nc
Specific Humidity 4-times Daily 28 levels /Datasets/ncep.reanalysis/spectral/shum.spec.yyyy.nc
Virtual Air Temperature 4-times Daily 28 levels /Datasets/ncep.reanalysis/spectral/vair.spec.yyyy.nc
Relative Vorticity 4-times Daily 28 levels /Datasets/ncep.reanalysis/spectral/vort.spec.yyyy.nc

Usage Restrictions:

  • None

Detailed Description:

  • The NCEP/NCAR Reanalysis 1 project is using a state-of-the-art analysis/forecast system to perform data assimilation using past data from 1948 to the present. A large subset of this data is available from PSL in its original 4 times daily format and as daily averages. However, the data from 1948-1957 is a little different, in the regular (non-Gaussian) gridded data. That data was done at 8 times daily in the model, because the inputs available in that era were available at 3Z, 9Z, 15Z, and 21Z, whereas the 4x daily data has been available at 0Z, 6Z, 12Z, and 18Z. These latter times were forecasted and the combined result for this early era is 8x daily. The local ingestion process took only the 0Z, 6Z, 12Z, and 18Z forecasted values, and thus only those were used to make the daily time series and monthly means here.


  • Please read the problem list before using the data.
  • There are no daily averages for the spectral data available from PSL.

Related File Naming & Structure Information:

File Names:

  • See individual sections. Data in /Datasets/ncep.reanalysis/, Datasets/ncep.reanalysis.dailyavgs/, /Datasets/ncep.reanalysis.derived/

Dataset Format and Size:

  • PSL standard NetCDF most are (packed).
    • All data are stored in netCDF files
    • The data are divided by variable and year into separate files
    • There are 205 files currently
    • Sizes range from 17 Kbytes to 331 Mbytes per variable per year
    • Current total of 54 Gbytes for 4xDaily
    • 4x daily data are available from ftp.cdc.noaa.gov in /Datasets/ncep.reanalysis/spectral/.
    • The 4x data files are quite large, so you may only be able to download them if you have a fast network connection.
    • The FORTRAN code readspec.f may be helpful in converting the coefficients to a regular grid.
  • If you would like datasets on a media such as tape, you will need to get them from another institution. NCAR (link) provides such a service for their datasets.

Missing Data:

  • Missing data is flagged with a value of -9.96921e+36f.


  • For dataset source, please cite:Kalnay et al.,The NCEP/NCAR 40-year reanalysis project, Bull. Amer. Meteor. Soc., 77, 437-470, 1996.
  • Please note: If you acquire NCEP Reanalysis data products from PSL, we ask that you acknowledge us in your use of the data. This may be done by including text such as NCEP Reanalysis data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at / in any documents or publications using these data. We would also appreciate receiving a copy of the relevant publications. This will help PSL to justify keeping the NCEP Reanalysis data set freely available online in the future. Thank you!


  • March, 1996 BAMS

Original Source:

  • NOAA National Center for Environmental Prediction


  • Physical Sciences Laboratory: Data Management
    325 Broadway
    Boulder, CO 80305-3328