Overview

This document provides an overview of the 2 m humidity data from Twentieth Century Reanalysis (20CRv3). The 20th Century Reanalysis Project is an effort led by NOAA's Physical Sciences Laboratory (PSL) and CIRES at the University of Colorado, supported by the Department of Energy (DOE), to produce reanalysis datasets spanning the entire 20th century and much of the 19th century. These reanalyses assimilate only surface observations of synoptic pressure into NOAA’s Global Forecast System, and prescribed sea surface temperature and sea ice distribution in order to estimate atmospheric variables, from the surface to the top of the atmosphere throughout the 19th and 20th centuries. 20CRv3 is version 3 of the project. For version 3, the ensemble mean and standard deviation for each value were calculated over a set of 80 analyses and short-term forecasts.

Provider's contact information

20CRv3 is developed by the NOAA's Physical Sciences Laboratory (PSL) and CIRES at the University of Colorado, supported by the Department of Energy (DOE).

For help with the dataset please contact

Gilbert P. Compo

CIRES, University of Colorado at Boulder, and Physical Sciences Laboratory, National Oceanic and Atmospheric Administration

gilbert.p.compo at noaa.gov

Laura C. Slivinski

CIRES, University of Colorado at Boulder, and Physical Sciences Laboratory, National Oceanic and Atmospheric Administration

laura.slivinski at noaa.gov

Licensing and citation

20CRv3 data are provided by several collaborative organizations. User registration and agreement to terms and conditions of data service usage are required individually for each organization.

Data at NCAR RDA is licensed under a Creative Commons Attribution 4.0 International Licence.

The following citation should be used for data downloaded from NCAR RDA:

" Slivinski, L. C., et al. 2019. NOAA-CIRES-DOE Twentieth Century Reanalysis Version 3. Research Data Archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory. https://doi.org/10.5065/H93G-WS83. Accessed† dd mmm yyyy.

†Please fill in the "Accessed" date with the day, month, and year (e.g., - 5 Aug 2011) you last accessed the data from the RDA. "

The following citation should be used for data downloaded from Physical Sciences Laboratory (PSL) or from National Energy Research Scientific Computing Center (NERSC):

Papers using the NOAA-CIRES-DOE Twentieth Century Reanalysis Project version 3 dataset are requested to include the following text in their acknowledgments: "Support for the 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.”

If you acquire 20th Century Reanalysis V3 data products from PSL, we are asked to acknowledge PSL by including also a text such as 20th Century Reanalysis V3 data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at / in any documents or publications using these data and send a copy of the relevant publications to:

Physical Sciences Laboratory: Data Management

NOAA/ESRL/PSL

325 Broadway

Boulder, CO 80305-3328

psl.data@noaa.gov

Spatial coverage and resolution:

20CRv3 data, is a global dataset. 20CRv3 has a Gaussian T-254 grid (approximately 75 km at the equator).

Variable name and units:

The following table summarizes the 2 m humidity data.

Temporal coverage and resolution:

On PSL website, 20CRv3.SI is available for years 1836-1980 and 20CRv3.MO is available for years 1981-2015 (the only differences between these two versions are the prescribed sea surface temperatures and dates of availability):

At NCAR RDA, 20CRv3 is available from:

The data is updated on an irregular base.

Information about observations (number, homogeneity)

These reanalyses assimilate only surface observations of synoptic pressure. Boundary conditions of pentad sea surface temperature and monthly sea ice concentration and time-varying solar, volcanic, and carbon dioxide radiative forcings are prescribed.

The surface pressure observations: ISPD version 4.7, made available through international cooperation facilitated by the Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative and working groups of the Global Climate Observing System and World Climate Research Program.

Sea Ice Concentration Boundary Condition: monthly HadISST2.3 sea ice (Slivinski et al., 2019; Titchner & Rayner 2014; Walsh et al., 2015)

Sea Surface Temperature Boundary Condition: prior to 1981(20CRv3.SI): 8 members of pentad interpolated to daily Simple Ocean Data Assimilation with Sparse Input (SODAsi) version 3 (SODAsi.3, Giese et al., 2016) seasonally adjusted to the 1981-2010 HadISST2.2 climatology. Regions where sea ice was ever indicated in HadISST2.3 are filled with: HadISST2.2 daily (1963+); HadISST2.1 monthly interpolated to daily (1850-1962); or the 1861–1891 HadISST2.1 climatology (1849 and earlier). 1981 and later (20CRv3.MO): 8 members of pentad interpolated to daily HadISST2.2 sea surface temperatures.

Methodology

20CRv3 assimilates only surface observations of synoptic pressure into an 80-member the coupled Global Forecast System land-atmospheric model with prescribed sea surface temperatures and sea ice concentration. A coupled one-dimensional thermodynamic sea-ice model is also used. Boundary conditions of pentad sea surface temperature and monthly sea ice concentration and time-varying solar, volcanic, and carbon dioxide radiative forcings are prescribed.

Forecast model: 20CRv3 uses the atmospheric model from the NCEP Global Forecast System v14.0.1 coupled with the Noah land surface model and 2.5-layer thermodynamic sea ice model (Compo et al., (2011). The forecast system is run at a resolution of T254 (approximately 75 km at the equator) with 64 vertical levels up to .3 mb and it has 80 individual ensemble members.

Assimilation model: The data assimilation algorithm is the Ensemble Square Root Filter (Whitaker and Hamill 2002) with 4D Incremental Analysis Update (4D-IAU; Bloom et al., 1996, Lei & Whitaker 2016). The snow relaxes to a monthly climatology (Saha et al., 2010) over 60 days.

Streams: Every 5th year a stream is produced for a continuous 5 year period. Stream years are 1835, 1840, ... , 2005, 2010. Stream year 2010 will be extended beyond 2015.

Information about the technical and scientific quality

There are three previous versions of the reanalysis: V1, V2, and V2c. Several adjustments were made to the model prior to implementation in the 20CRv3 system. Updates to the parameterizations are described in Saha et al. (2010) and include revised solar radiation transfer, boundary layer vertical diffusion, cumulus convection, and gravity wave drag parameterizations. In addition, the cloud liquid water is a prognostic quantity with a simple cloud microphysics parameterization. Another important improvement is in the resolution and ensemble size. Previous 20CR versions were using a 56-member ensemble with a coarser spatial resolution (T62 28 levels), while the 20CRv3 is using 80 ensemble members with a finer spatial resolution (T254 64 levels). 20CRv3 also assimilates a larger set of observations and includes an improved data assimilation system relative to its predecessor 20CRv2c.

Observations are first grossly tested for quality control: if the observation is outside the range 850 and 1090 hPa, or if the absolute difference between the observation and the first guess value is greater than 3.2 times the square root of the sum of the forecast ensemble variance and the observation error variance, the observation is rejected. (Slivinski et al., 2018). They are then subject to adaptive quality control and adaptive localization control.

Limitations and strengths for application in North Canada

Key Strengths: Length of record and estimates of uncertainty

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.

References to documents describing the methodology or/and the dataset

Compo, G.P., J.S. Whitaker, P.D. Sardeshmukh, N. Matsui, R.J. Allan, X. Yin, B.E. Gleason, R.S. Vose, G. Rutledge, P. Bessemoulin, S. Brönnimann, M. Brunet, R.I. Crouthamel, A.N. Grant, P.Y. Groisman, P.D. Jones, M. Kruk, A.C. Kruger, G.J. Marshall, M. Maugeri, H.Y. Mok, Ø. Nordli, T.F. Ross, R.M. Trigo, X.L. Wang, S.D. Woodruff, and S.J. Worley, 2011: The Twentieth Century Reanalysis Project. Quarterly Journal of the Royal Meteorological Society, 137(654), 1-28, DOI: 10.1002/qj.776.

Slivinski, L. C.,G. P. Compo, P.D. Sardeshmukh, J. S. Whitaker, C. McColl, R. J. Allan, P. Brohan, X. Yin, C. A. Smith, L. J. Spencer, R. S. Vose, M. Rohrer, R. P. Conroy, D. C. Schuster, J. J. Kennedy, L. Ashcroft, S. Brönnimann, M. Brunet, D. Camuffo, R. Cornes, T. A. Cram, F. Domínguez-Castro, J. E. Freeman, J. Gergis, E. Hawkins, P. D. Jones, H. Kubota, T. C. Lee, A. M. Lorrey, J. Luterbacher, C. J. Mock, R. K. Przybylak, C. Pudmenzky, V. C. Slonosky, B. Tinz, B. Trewin, X. L. Wang, C. Wilkinson, K. Wood, and P. Wyszyński , 2021: An Evaluation of the Performance of the Twentieth Century Reanalysis Version 3. Journal of Climate 34, 4, 1417-1438, https://doi.org/10.1175/JCLI-D-20-0505.1

Link to download the data and format of data:

20CRv3 data are available at several organizations.

At NOAA/PSL, the ensemble mean and the ensemble uncertainty files are available in netCDF4 format: https://psl.noaa.gov/data/gridded/data.20thC_ReanV3.monolevel.html

At National Center for Atmospheric Research (NCAR), the ensemble mean and the ensemble uncertainty files are available in netCDF4 format: https://rda.ucar.edu/datasets/ds131.3/

At NERSC Science Gateway, data for every member of 20CRv3 are available in netCDF4 format: https://portal.nersc.gov/project/20C_Reanalysis/