NOAA 20th-Century Reanalysis, Version 2 and 2c

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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 simulations of the 20th century, with emphasis on the statistics of daily weather. The analyses are generated by assimilating only surface pressures and using monthly SST and sea ice distributions as boundary conditions within a 'deterministic' Ensemble Kalman Filter (EKF). A unique feature of the 20CR is that estimates of uncertainty are derived using a 56 member ensemble. Overall, the quality is approximately that of current three-day NWP forecasts.

20th Century Reanalysis Version v2c uses the same model as version 2 with new sea ice boundary conditions from the COBE-SST2 (Hirahara et al. 2014), new pentad Simple Ocean Data Assimilation with sparse input (SODAsi.2) sea surface temperature fields, and additional observations from ISPD version 3.2.9.

As of 2020, NOAA has released 20CRv3, which covers the period 1806-2015. More information about 20CRv3 will be added to the Climate Data Guide soon.

Key Strengths

Key Strengths

Length of record

Estimates of uncertainty

Key Limitations

Key Limitations

As with all reanalyses, users should take care in interpreting long-term trends - inconsistencies between 20CR and other data have been reported, especially on a regional scale

Cite this page

Acknowledgement of any material taken from or knowledge gained from this page is appreciated:

National Center for Atmospheric Research Staff (Eds). Last modified "The Climate Data Guide: NOAA 20th-Century Reanalysis, Version 2 and 2c.” Retrieved from on 2024-07-21.

Citation of datasets is separate and should be done according to the data providers' instructions. If known to us, data citation instructions are given in the Data Access section, above.

Acknowledgement of the Climate Data Guide project is also appreciated:

Schneider, D. P., C. Deser, J. Fasullo, and K. E. Trenberth, 2013: Climate Data Guide Spurs Discovery and Understanding. Eos Trans. AGU, 94, 121–122,

Key Figures

Climate Data Guide Image: NOAA 20th-Century Reanalysis, Version 2

Air temperature at the lowest model level, sigma.995, from the 20CRV2 ensemble mean. Averaged for 1951-1980. Credit: Climate Data Guide.

Other Information

Years of record
Data time period extended
No, data set not being extended
Sub-daily, Daily, Monthly
Input Data

surface and sea level pressure, sea surface temp., sea-ice concentration

Vertical Levels:
Missing Data Flag
Spatially complete
Ocean or Land
Ocean & Land
Spatial Resolution

2°x2°, 28 levels 10 hPA top

Model Resolution (reanalysis)

T62 28 levels

Data Assimilation Method
Model Vintage (reanalysis)