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NCEP/NCAR Reanalysis Monthly Means and Other Derived Variables

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

Brief Description:

  • NCEP/NCAR Reanalysis Monthly Means and Other Derived Variables..

Temporal Coverage:

  • Daily and Monthly Values for 1948/01 - present.
  • Long term monthly means, derived from data for years 1968 - 1996.

Spatial Coverage:

  • T62 Gaussian grid with 192x94 points
  • 88.542N-88.542S, 0E-358.125E
Temporal coverage:
  • 1/1/1958 - 11/2001 monthly means (not in CDAS update)
  • Daily psi and chi: Jan 1 1948 to "present".
  • Long-Term term monthly mean files are averaged over 1968-1996


  • 2 Sigma levels: 0.995,0.2101 for monthly means and monthly LTMs.
  • 5 sigma levels 0.995 , 0.8458 , 0.2582 , 0.2101 , 0.1682 for chi & psi in daily, daily LTMs, and monthly means forms.

Update Schedule:

  • Monthly and daily for daily data.

Download/Plot Data: (Download Issues)

Variables: File Units Statistics Available
Divergence div 1./s mon mean,ltm
Relative Vorticity vort 1./s mon mean,ltm
Derived File Units Statistics Available
Velocity Potential chi m*m/s mon mean,ltm,day
Streamfunction psi m*m/s mon mean,ltm,day

Availability and Usage Restrictions:

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.


  • None

Related File Naming & Structure Information:

File Names:

  • var.time.stat.nc   (In directory: /Datasets/ncep.reanalysis.derived/sigma/)

Dataset Format and Size:

  • All data are stored in netCDF files
  • The data are divided by variable and type
  • There are 119 files currently
  • Sizes range are 1.7 Mbytes and 253.5 Mbytes
  • Current total of about 8.2 Gbytes

Missing Data:

  • Missing data is flagged with a value of -9.96921e+36f for most files.
  • Chi & Psi monthly LTMs use 1.0e+30f.


  • 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 Derived 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 Derived 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 Derived data set freely available online in the future. Thank you!



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