American Reanalysis - NCEP/NCAR Reanalysis 1



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Data access via file system: /data/icdc/reanalyses/ncep_reanalysis1



The National Centers for Atmospheric Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) have accomplished different re-analysis projects which aim on the generation of global data sets for a long time period for different atmospheric parameters. The here presented NCEP1 reanalysis has been used in numerous publications and has, therefore, in addition to the recent re-analysis products the advantage of very long time series.

The re-analysis is created with a model similar to the one used for weather forcasts. This model is initialised with measured data from different sources, including observations from weather stations, ship, aircraft, radiosondes, and satellite. Using one model for the whole re-analysis period generates homogeneous data that can be used for long term studies.

NCEP/NCAR has produced several re-analyses, that are described on their web-page. Here we give an introduction to the NCEP/NCAR Reanalysis I (1948-present). This free data set is updated continuously and has therefore many users worldwide. There is a large number of available parameters in several height levels, NCEP divided into 7 groups on its website, after level or properties:

Using the NCEP search funktioncan also be convenient to search for parameters in various data sets. ICDC has a selection of ground-level parameters put together, which are listed in the following table.

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Name Unit Level
Air temperature (air) K 2 m
Minimum Temperature (tmin) K 2 m
Maximum Temperature (tmax) K 2 m
Latent Heat Net Flux (lhtfl) W/m^2 Surface
Net Longwave Radiation Flux (nlwrs) W/m^2 Surface
Relative humidity (rhum) % Surface (0.9950 sigma level)
Sensible Heat Net Flux (shtfl) W/m^2 Surface
Volumetric Soil Moisture (soilw) fraction between 0-10 cm below ground level
Soil Temperature (tmp) K between 0-10 cm below ground level
Specific Humidity (shum) kg/kg 2 m
Convective Precipitation Rate (cprat) Kg/m^2/s Surface
Surface Pressure (pres) Pa Surface
Total cloud cover (tcdc) % Entire Atmosphere Considered As a Single Layer
u-wind (uwnd) and v-wind (vwnd) m/s 10 m

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Coverage, spatial and temporal resolution

Period and temporal resolution:

  • 1948/01/01 to now
  • 6-hourly, daily and monthly

Coverage and spatial resolution:

  • Global
  • Spatial resolution: about 1.875° x 1.875°, Gaussian grid, (for some parameters 2.5° x 2.5°)
  • Geographic longitude: 0.0°E to 358.125°E
  • Geographic latitude: -88.542°N to 88.542°N
  • Dimension: 192 columns x 94 rows (for some parameters 144 x 72)


  • netCDF4

Data quality

Four categories are defined by Kalnay et al. :

  • A is for variables that are mainly influenced by observational data. These variables have the best quality.
  • B is for variables that are influenced by observational data and dependent on the model. They have less quality than A.
  • C is for variables that are not directly influenced by observations but solely based on the model. They are less reliable.
  • D is for variables that are not from the model but from external sources, like for example the land-sea-mask.

The NCEP/NCAR Reanalyse Problem List contains all known problems related to the re-analysis data sets.


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Remon Sadikni, ICDC

remon.sadikni (at) uni-hamburg.de


Physical Sciences Division: Data Management


325 Broadway

Boulder, CO 80305-3328https://www.klimacampus.de/?id=

esrl.psd.data (at) noaa.gov

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Data Citation

Kalnay et al.,The NCEP/NCAR 40-year reanalysis project, Bull. Amer. Meteor. Soc., 77, 437-470, 1996

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