Reanalysis

Comprehensive weather and climate datasets, reanalyses assimilate a variety of observations of the atmosphere, land surface, and ocean into a forecast model to provide a dynamically consistent estimate of the climate state at each time step.

Below is the atmospheric reanalysis overview page, which summarizes the attributes of the major atmospheric reanalyses. This section also includes selected oceanic reanalyses, although an overview is not available yet.

To find a specific reanalysis, jump to the search box below or click your desired reanalysis from among the blue sub-category buttons.

To see only the reanalyses pages accompanied by in-depth commentary, select the "Datasets with guidance" button when using the search box.

Climate datasets

Has expert guidance
Climate Forecast System Reanalysis (CFSR) Climate Forecast System Reanalysis (CFSR)
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The CFSR is a third generation reanalysis product. It is a global, high resolution, coupled atmosphere-ocean-land surface-sea ice system designed to provide the best estimate of the state of these coupled domains over this period. The CFSR includes (1) coupling…

Main variables and Earth System components

Atmosphere Air Temperature Geopotential Height Precipitable water Ocean
  • Experts contributing reviews

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JRA-55 JRA-55
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Spanning 1958-present, JRA-55 is the longest third-generation reanalysis that uses the full observing system (in contrast, products like ERA-20C and NOAA 20CR assimilate a very limited set of observations while NCEP R1 uses an antiquated model and assimilation…

Main variables and Earth System components

Atmosphere Air Temperature Geopotential Height Precipitable water
    • Timestep

    • Sub-daily, Monthly
    • Collections

    • None
ERA5 atmospheric reanalysis ERA5 atmospheric reanalysis
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ERA5, the successor to ERA-Interim,  provides global, hourly estimates of atmospheric variables, at a horizontal resolution of 31 km and 137 vertical levels from the surface to 0.01 hPa. Produced by ECMWF, ERA5 presently extends back to 1979; it will ultimately…

Main variables and Earth System components

Atmosphere
Atmospheric Reanalysis: Overview & Comparison Tables Atmospheric Reanalysis: Overview & Comparison Tables
  • Years of record

Reanalysis a systematic approach to produce data sets for climate monitoring and research. Reanalyses are created via an unchanging ("frozen") data assimilation scheme and model(s) which ingest all available observations every 6-12 hours over the period being…

Main variables and Earth System components

Atmosphere
Climate Data Guide NCEP Reanalysis (R2)
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NCEP-DOE Reanalysis II (R2) is an improved version of the NCEP-NCAR Reanalysis I (R1). The improvements include an updated model with better physical parameterizations, assorted data assimilation errors were fixed and additional data were included. Still, it…

Main variables and Earth System components

Atmosphere Air Temperature Geopotential Height Precipitable water
    • Timestep

    • Sub-daily, Daily, Monthly
    • Collections

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  • Experts contributing reviews

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SODA:  Simple Ocean Data Assimilation SODA: Simple Ocean Data Assimilation
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The Simple Ocean Data Assimilation, or SODA, analysis is an ocean reanalysis data set consisting of gridded variables for the global ocean, as well as several derived fields. The goal is to provide an improved estimate of ocean state from those based solely on…

    • Timestep

    • Monthly
    • Collections

    • None
  • Experts contributing reviews

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NASA's MERRA2 reanalysis NASA's MERRA2 reanalysis
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The Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) is a global atmospheric reanalysis produced by the NASA Global Modeling and Assimilation Office (GMAO). It spans the satellite observing era from 1980 to the present. The…

Main variables and Earth System components

Atmosphere Aerosols Air Temperature Geopotential Height Precipitable water
    • Timestep

    • Sub-daily, Daily, Monthly
    • Collections

    • None
ERA-Interim ERA-Interim
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Using a much improved atmospheric model and assimilation system from those used in ERA-40, ERA-Interim represents a third generation reanalysis. Several of the inaccuracies exhibited by ERA-40 such as too-strong precipitation over oceans from the early 1990's…

NCEP-NCAR (R1): An Overview NCEP-NCAR (R1): An Overview
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NCEP-NCAR (R1) is the original reanalysis effort. It uses a frozen global state-of-the-art global data assimilation system (as of 11 January 1995). The original database was enhanced (additional, quality checked datasets) by NCAR's Data Support Section.…

Main variables and Earth System components

Atmosphere Air Temperature Geopotential Height
  • Experts contributing reviews

  • None
GODAS: NCEP Global Ocean Data Assimilation System GODAS: NCEP Global Ocean Data Assimilation System
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GODAS is a real-time ocean analysis and a reanalysis. It is used for monitoring, retrospective analysis as well as for providing oceanic initial conditions for the CFS. Both temperature and synthetic salinity profiles are assimilated in a 3DVAR scheme.…

  • Experts contributing reviews

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ERA40 ERA40
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ERA 40 is a second generation reanalysis. It is the first reanalysis to directly assimilate satellite radiance data (TOVS, SSM/I, ERS and ATOVS). Cloud Motion Winds are also used. The result is better circulation over the tropics and southern hemisphere.…

Main variables and Earth System components

Atmosphere Air Temperature Geopotential Height Water Vapor
  • Experts contributing reviews

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NASA MERRA NASA MERRA
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The Modern Era Retrospective-Analysis for Research and Applications (MERRA) was undertaken by NASA’s Global Modeling and Assimilation Office with two primary objectives: to place observations from NASA’s Earth Observing System satellites into a climate context…

Main variables and Earth System components

Atmosphere Air Temperature Geopotential Height Precipitable water Water Vapor
  • Experts contributing reviews

  • None
NOAA 20th-Century Reanalysis, Version 2 and 2c NOAA 20th-Century Reanalysis, Version 2 and 2c
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The Twentieth Century Reanalysis (20CR) provides a comprehensive global atmospheric circulation data set spanning 1850-2014. Its chief motivation is to provide an observational validation data set, with quantified uncertainties, for assessing climate model…

Main variables and Earth System components

Atmosphere Air Temperature Geopotential Height
  • Experts contributing reviews

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ERA-20C: ECMWF's atmospheric reanalysis of the 20th century (and comparisons with NOAA's 20CR) ERA-20C: ECMWF's atmospheric reanalysis of the 20th century (and comparisons with NOAA's 20CR)
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The ECMWF's first atmospheric reanalysis of the 20th Century, ERA-20C, provides a long, gridded dataset of many climate variables, spanning 1900-2010.  Observations assimilated include surface pressures from the International Surface Pressure Databank v3.2.6…

Main variables and Earth System components

Atmosphere Multiple variables
ORAS4: ECMWF Ocean Reanalysis and derived ocean heat content ORAS4: ECMWF Ocean Reanalysis and derived ocean heat content
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ECMWF's current ocean reanalysis uses a sophisticated data assimilation methodology which includes a model bias correction. The ocean model used is forced by atmospheric daily surface fluxes, relaxed to SST and bias corrected. The Balmaseda et al (QJRMS 2013)…

  • Experts contributing reviews

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CMCC Global Ocean Reanalysis System (C-GLORS) CMCC Global Ocean Reanalysis System (C-GLORS)
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"The CMCC Global Ocean Physical Reanalysis System (C-GLORS) is used  to simulate the state of the ocean in the last decades. It consists of a variational data assimilation system (OceanVar), capable of assimilating all in-situ observations along with altimetry…

    • Timestep

    • Daily, Monthly, Weekly
    • Collections

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Southern Ocean State Estimate (SOSE) Southern Ocean State Estimate (SOSE)
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The Southern Ocean State Estimate (SOSE) is a model-generated best fit to Southern Ocean observations.  As such, it provides a quantitatively useful climatology of the mean-state of the Southern Ocean.  Technically, SOSE is a solution to the MITgcm.  SOSE is a…

NCEP NARR NCEP NARR
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A high resolution (32km x 29 pressure levels) data set focused upon the North American Region. Relative to the NCEP-DOE (R2) it has a much improved land-hydrology, diurnal cycle and land-atmosphere interaction. As such, it can be considered a second generation…

Main variables and Earth System components

Atmosphere Air Temperature Geopotential Height Precipitable water Land
    • Timestep

    • Climatology, Sub-daily, Monthly
    • Collections

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  • Experts contributing reviews

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Arctic System Reanalysis (ASR) Arctic System Reanalysis (ASR)
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The Arctic System Reanalysis is a multi-agency, university-led retrospective analysis (reanalysis) of the Greater Arctic. ASR is produced using high-resolution versions of the Polar Weather Forecast Model (PWRF) and the WRF-VAR and High Resolution Land Data…

Main variables and Earth System components

Atmosphere Cryosphere Land Soil Moisture
    • Timestep

    • Sub-daily, Monthly
    • Collections

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  • Experts contributing reviews

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ERA-Interim: derived components ERA-Interim: derived components
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Era-Interim data are used to derive monthly mass, moisture and energy budget products. Each term is available. Atmospheric energy, mass, and moisture budgets can be computed by vertically integrating reanalysis fields and employing suitable corrections (e.g.…

Main variables and Earth System components

Atmosphere Budget Evaporation-Precipitation
  • Experts contributing reviews

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Simplistic Overview of Reanalysis Data Assimilation Methods Simplistic Overview of Reanalysis Data Assimilation Methods
  • Years of record

Data assimilation is the process of combining observations from a wide variety of sources and forecast output from a weather prediction model. The resulting analysis is considered to be the 'best' estimate of the state of the atmosphere at a particular instant…

Main variables and Earth System components

Atmosphere
    • Formats

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    • Domain

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  • Experts contributing reviews

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CERA-20C:  ECMWF's Coupled Ocean-Atmosphere Reanalysis of the 20th Century CERA-20C: ECMWF's Coupled Ocean-Atmosphere Reanalysis of the 20th Century
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The CERA-20C is a global, coupled reanalysis spanning 1901-2010 with a focus on low-frequency climate variability.  Similar to ERA-20C, the surface observations assimilated include surface pressures from the International Surface Pressure Databank v3.2.6 and…

Main variables and Earth System components

Atmosphere Multiple variables Cryosphere Sea Ice Concentration Ocean
    • Timestep

    • Sub-daily, Daily, Monthly
    • Collections

    • None
JRA-25 JRA-25
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JRA-25 is a second generation reanalysis product. The model and data assimilation are from the operational system in April 2004. It was the first reanalysis to assimilate wind profiles around tropical cyclones deduced from best-track data, resulting in improved…

Main variables and Earth System components

Atmosphere Air Temperature Geopotential Height Precipitable water
  • Experts contributing reviews

  • None
Climate Data Guide ERA-15
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The ERA-15 production system generated re-analyses for 15 years (1979-1993)  using a special version of their 1995 operational data assimilation system and model. The resulting analyses include full model resolution analyses or  reduced resolution analyses and…

Main variables and Earth System components

Atmosphere