20CR (v3)¶

NOAA-CIRES-DOE Twentieth Century Reanalysis Version 3

Discontinued

At a glance¶

Note on period: The released period is January 1836 to December 2015, with 1806–1835 as an experimental extension (released in 2021). In the NCAR metadata, the full range is 1805-12-31 18 UTC to 2016-01-01 00 UTC. Uncertainty is very large in the early 19th century, when observations are sparse, so always look at the ensemble spread.

Overview¶

The Twentieth Century Reanalysis assimilates only surface observations of synoptic pressure into NOAA's Global Forecast System and prescribes sea surface temperature and sea-ice distribution, producing 3-hourly estimates of the global atmosphere from the early 19th century to 2015. Using a single observation type avoids artificial changes from the introduction of satellite and upper-air data, and the 80-member ensemble filter provides an uncertainty estimate for every analysis. It is mainly used for historical extreme events, long-term circulation variability, and the pre-1940 period that other reanalyses do not cover.

What changes with the successor¶

20CR v2c → 20CR v3¶

Transition: 2019

Version 3 moves to the autumn 2017 operational GFS, raising the resolution from T62 to T254, increases the ensemble from 56 to 80 members, and adds many more surface pressure observations from ISPD version 4.7. Adaptive covariance inflation and localization give more realistic uncertainty (ensemble spread) estimates, and the mid-19th-century sea-level pressure bias and precipitation spin-up problems are reduced. The record now starts in 1836 (1806 experimentally).

Sources: Slivinski et al. (2019), Towards a more reliable historical reanalysis — 20CRv3, QJRMS, 145, 2876–2908 · NSF NCAR GDEX — 20CR Version 3 (d131003) · NSF NCAR GDEX — 20CR Version 2c (d131002) · reanalyses.org — 20CRv3 system details (compiled by the 20CR team) · reanalyses.org — New 20CR DA system presentation (comparison with the previous system) · NCAR Climate Data Guide — 20CR Version 2 and 2c · NOAA PSL news — Version 3 of the 20CR dataset will provide a 180-year history of the weather (2019-08-16)

Available variables¶

Main variables from the NOAA PSL netCDF files (OPeNDAP attributes). Short names are the in-file names; the PSL folder name is given in each group heading. Folder names ending in SI hold 1806–1980 files and MO hold 1981–2015 files (e.g. prsSI, prsMO). Spread files follow the same layout under spreads/.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

Pressure levels (prsSI, prsMO; 3-hourly, 1000–1 hPa)¶

Near surface (2mSI, 2mMO, 10mSI, 10mMO)¶

Single level and column (miscSI, miscMO)¶

Accumulations and snow (accumsSI, accumsMO; 3-hourly accumulation)¶

Surface fluxes (sfcFlxSI, sfcFlxMO)¶

The full variable list is in the official documentation.

How to get the data¶

• NOAA PSL — Twentieth Century Reanalysis Project page — Overview, documentation for each version, links to plotting tools
• NOAA PSL download server (20CR v3) — Direct HTTPS download No login needed
  • No account needed. netCDF files by variable and year; daily means are in Dailies/, monthly means in Monthlies/ and the ensemble spread in spreads/.
• NOAA PSL THREDDS / OPeNDAP (20CR v3) — Remote access via OPeNDAP No login needed
• NSF NCAR GDEX — 20CR Version 3 (d131003) — Web download / subsetting
  • Ensemble mean and spread, netCDF4, about 105 TB. Dataset DOI 10.5065/H93G-WS83, CC BY 4.0.
• NERSC 20C Reanalysis portal (individual members) — Web download (some data on HPSS tape) No login needed
  • Use this when you need the analysis and forecast fields of each of the 80 members. Data come as tar bundles by variable and year.

Example code¶

Data from 1981 onward are in the MO folders; data up to 1980 are in the SI folders.

import xarray as xr

base = "https://psl.noaa.gov/thredds/dodsC/Datasets/20thC_ReanV3"
slp = xr.open_dataset(f"{base}/miscMO/prmsl.2014.nc")["prmsl"]   # Pa, 3-hourly ensemble mean
print(slp.sel(lat=37.5, lon=127.0, method="nearest").resample(time="1D").mean())

Practical tips¶

• Reliability varies widely with observation density, even at the same time. Do not use the ensemble mean alone; check the spread in the spreads/ folder and avoid interpreting regions where the spread approaches the size of climate variability.
• The SST boundary condition is SODAsi.3 through 1980 and HadISST2.2 from 1981, which is why the PSL folders are split into SI and MO. Analyses spanning 1980/1981 must read both folders, and should check for a discontinuity at that point.
• Version 3 uses different variable abbreviations from versions 2 and 2c, as the NERSC portal also points out. Check variable names first when reusing old scripts.
• The developers' evaluation shows systematic biases in tropical precipitation and time-varying biases in Southern Hemisphere high-latitude pressure. For these topics, cross-check results against other long reanalyses such as ERA-20C.

Notices and change history¶

References for your paper¶

Dataset citation¶

NCAR GDEX 20CR v3 (d131003) — DOI 10.5065/H93G-WS83

Reference papers¶

20CR v3 system paper — DOI 10.1002/qj.3598

@article{slivinski2019_20crv3,
  author  = {Slivinski, Laura C. and Compo, Gilbert P. and Whitaker, Jeffrey S. and Sardeshmukh, Prashant D. and Giese, Benjamin S. and McColl, Chesley and Allan, Rob and Yin, Xungang and Vose, Russell and Titchner, Holly and others},
  title   = {Towards a more reliable historical reanalysis: Improvements for version 3 of the Twentieth Century Reanalysis system},
  journal = {Quarterly Journal of the Royal Meteorological Society},
  volume  = {145},
  number  = {724},
  pages   = {2876--2908},
  year    = {2019},
  doi     = {10.1002/qj.3598}
}

20CR v3 performance evaluation (optional) — DOI 10.1175/JCLI-D-20-0505.1

Original 20CR project paper (optional) — DOI 10.1002/qj.776

Acknowledgements¶

PSL asks papers using version 3 to include: "Support for the NOAA-CIRES-DOE Twentieth Century Reanalysis Project version 3 dataset is provided by the U.S. Department of Energy, Office of Science Biological and Environmental Research (BER), by the National Oceanic and Atmospheric Administration Climate Program Office, and by the NOAA Physical Sciences Laboratory." PSL also asks you to acknowledge PSL as the data provider and to send a copy of the relevant publications.

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• NOAA PSL — Twentieth Century Reanalysis Project
• NOAA PSL — 20CR v3 dataset page
• reanalyses.org — 20CRv3 system details
• NCAR Climate Data Guide — 20CR Version 2 and 2c