Reanalysis datasets and variables available from page

Currently, only pressure level variables are available. The different datasets have different analyses levels so you may need to consider that when choosing differences. The dataset are at different resolutions. Differences are computed by interpolating the lowest res dataset of the 2 being compared to the resolution of the higher res and subtracting. Anomalies are based on the climo from each reanalyses dataset separately. Units have been changed so the datasets can be compared. Climatologies only exist for NCEP 1, NCEP 2 and 20CR at this time.

For more information and discussion of various atmospheric and oceanic reanalyses, see the "Reanalysis Intercomparison and Observations Wiki" at

Dataset Availability. More data may be available at the source.

DatasetStart DataEnd DateClimo Available
NCEP/NCAR Reanalysis Jan 1948Dec 20111981-2010
NCEP/DOE Reanalysis IIJan 1979Dec 20111981-2010
20CRJan 1871Dec 20101981-2010
MERRAJan 1979Dec 20111981-2010
ERA-InterimJan 1979Dec 20101981-2010
  • NCEP/NCAR Reanalysis I 1948-present (NCEP R1 home page)

    This reanalysis was the first of it's kind for NOAA. NCEP used the same climate model that were initialized with a wide variety of weather observations: ships, planes, RAOBS, station data, satellite observations and many more. By using the same model, scientists can examine climate/weather statistics and dynamic processes without the complication that model changes can cause. The dataset is kept current using near real-time observations.
  • NCEP/DOE Reanalysis II (1979-2010)

    NCEP produced a second version of their first reanalysis starting from the beginning of the major satellite era. More observations were added, assimilation errors were corrected and a better version of the model was used.
  • 20th Century Reanalysis (V2) 1871-2010 (20CR Home page)

    The 20th Century Reanalysis version 2 dataset contains global weather conditions and their uncertainty in six hour intervals from the year 1871 to 2010. Surface and sea level pressure observations are combined with a short-term forecast from an ensemble of integrations of an NCEP numerical weather prediction model using the recently developed Ensemble Kalman Filter technique to produce an estimate of the complete state of the atmosphere, and the uncertainty in that estimate. Additional observations and a newer version of the NCEP model that includes time-varying CO2 concentrations, solar variability, and volcanic aerosols are used in version 2. The long time range of this dataset allows scientists to examine better long time scale climate processes such as the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation as well as looking at the dynamics of historical climate and weather events. Verification tests have shown that using only pressure creates reasonable atmospheric fields up to the tropopause. Additional tests suggest some correspondence with observed variations in the lower stratosphere.
  • NASA Modern Era Reanalysis for Research and Applications (MERRA): 1979-present (MERRA Home page)

    MERRA is a NASA reanalysis for the satellite era using a major new version of the Goddard Earth Observing System Data Assimilation System Version 5 (GEOS-5) produced by the NASA GSFC Global Modeling and Assimilation Office (GMAO). The Project focuses on historical analyses of the hydrological cycle on a broad range of weather and climate time scales and places the NASA EOS suite of observations in a climate context.