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 lower res dataset of the two 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 For references/citations please go to the wiki page for a current list.

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

DatasetStart DataEnd DateClimo Available
NCEP/NCAR Reanalysis Jan 1948near present1981-2010
NCEP/DOE Reanalysis IIJan 1979Jun 20161981-2010
20CRV2cJan 1851Dec 20141981-2010
20CRJan 1871Dec 20121981-2010
MERRAJan 1979Jan 20161981-2010
MERRA-2Jan 1980Dec 20161981-2010
ERA-InterimJan 1979Dec 20161981-2010
CFSRJan 1979present1981-2010
ERA-20CJan 1900Dec 20101981-2010
  • NCEP/NCAR Reanalysis I 1948-present (NCEP R1 home page)

    This reanalysis was the first of its kind for NOAA. NCEP used the same climate model that was 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 (1979-2011)

    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.
  • NASA Modern Era Reanalysis for Research and Applications (MERRA-2): 1980-present (MERRA Home page)

    The Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) provides data beginning in 1980. It was introduced to replace the original MERRA dataset because of the advances made in the assimilation system that enable assimilation of modern hyperspectral radiance and microwave observations, along with GPS-Radio Occultation datasets. It also uses NASA ozone observations after 2005. Additional advances in both the GEOS-5 model and the GSI assimilation system are included in MERRA-2. Spatial resolution remains about the same (about 50 km in the latitudinal direction) as in MERRA. Along with the enhancements in the meteorological assimilation, MERRA-2 takes some significant steps towards GMAO’s target of an Earth System reanalysis. MERRA-2 is the first long-term global reanalysis to assimilate space-based observations of aerosols and represent their interactions with other physical processes in the climate system. MERRA-2 includes a representation of ice sheets over (say) Greenland and Antarctica.
  • ERA-Interim: 1979-present (ERA-Interim Home page)

    ERA-Interim was originally planned as an 'interim' reanalysis in preparation for the next-generation extended reanalysis to replace ERA-40. It uses a December 2006 version of the ECMWF Integrated Forecast Model (IFS Cy31r2). It originally covered dates from 1 Jan 1989 but an additional decade, from 1 January 1979, was added later. ERA-Interim is being continued in real time. The spectral resolution is T255 (about 80 km) and there are 60 vertical levels, with the model top at 0.1 hPa (about 64 km). The data assimilation is based on a 12-hourly four-dimensional variational analysis (4D-Var) with adaptive estimation of biases in satellite radiance data (VarBC). With some exceptions, ERA-Interim uses input observations prepared for ERA-40 until 2002, and data from ECMWF's operational archive thereafter. An pen-access journal article describing the ERA-Interim reanalysis is now available from the Quarterly Journal of the Royal Meteorological Society and should be used as the citation.
  • ERA-20C: 1900-2010 (ERA-20C Home page)

    ERA-20C is ECMWF's first atmospheric reanalysis of the 20th century, from 1900-2010. It assimilates observations of surface pressure and surface marine winds only. It is an outcome of the ERA-CLIM project.