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NOAA/ESRL 20th Century Reanalysis – V2 / V2c

Monolevels: 6-hourly

The NCEP-NCAR Reanalysis product starts from 1948, leaving many important climate events such as 1930's dust bowl droughts uncovered. To expand the coverage of global gridded reanalyses, the 20th Century Reanalysis Project is an international effort led by Physical Science Division and the University of Colorado CIRES Climate Diagnostics Center to produce a comprehensive global atmospheric circulation dataset spanning the twentieth century, assimilating only surface pressure reports and using observed monthly sea-surface temperature and sea-ice distributions as boundary conditions. The observations have been assembled through international cooperation under the auspices of the Atmospheric Circulation Reconstructions over the Earth initiative (ACRE), and working groups of GCOS and WCRP. It is chiefly motivated by a need to provide an observational dataset with quantified uncertainties for validations of climate model simulations of the twentieth century on all time-scales, with emphasis on the statistics of daily weather. The Project uses an Ensemble Kalman Filter data assimilation method with background ‘first guess’ fields supplied by an ensemble of forecasts from a global numerical weather prediction model. This directly yields a global analysis every 6 hours as the most likely state of the atmosphere, and also an uncertainty estimate of that analysis. Intercomparisons with independent radiosonde data indicate that the reanalyses are generally of high quality. The quality in the extratropical Northern Hemisphere throughout the century is similar to that of current three-day operational NWP forecasts. Intercomparisons over the second half-century of these surface-based reanalyses with other reanalyses that also make use of upper-air and satellite data are equally encouraging.

Citation:

• Please acknowledge usage of the datasets by including text such as 20th Century Reanalysis V2c data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at http://www.esrl.noaa.gov/psd/ in any documents or publications using these data.

Detailed Description:

• Observations (Pressure): ISPD version 3.2.9. The surface pressure observations have been 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 Programme.
• Sea Surface Temperature Boundary Condition: prior to 2013: 18 members of pentad Simple Ocean Data Assimilation with Sparse Input (SODAsi) version 2 (SODAsi.2, Giese et al. 2015) with the high latitudes (>60) corrected to COBE-SST2 (Hirahara et al. 2014). 2013 onwards, NOAA OI SST V2 High Resolution Dataset (Reynolds et al. 2007).
• Sea Ice Concentration Boundary Condition: monthly COBE-SST2 sea ice (Hirahara et al. 2014).
• Model: NCEP GFS 2008ex (Compo et al. 2011) but with sea ice concentration specification down to fractions of 0.15 permitted. Previously fraction was truncated at 0.5. Additionally, the sea ice concentration misspecification noted in Compo et al. (2011) is corrected.
• Assimilation: Ensemble Filter. Same algorithm as in 20CRv2 and as described in Compo et al. (2011), Compo et al. (2006), Whitaker et al. (2004).
• Streams: As in Compo et al. 2011, every 5th year is produced in parallel for a continuous 5 year stream that started from November of stream year-1. Stream years are 1850,1855,...,2000, 2005. Released data start in January of stream year + 1, e.g., 1851 to 1855, 1856 to 1860, ..., 2001 to 2005. stream year 2005 is extended to 2011 and will be extended beyond.
• Additional details: Compo, G.P., J.S. Whitaker, P.D. Sardeshmukh, B. Giese, and P. Brohan, 2015: Intercomparison of an improved 20th Century Reanalysis version "2c" (1850-2012), American Meteorological Society Annual meeting, Phoenix, AZ, January 2015. Presentation.
• Model Notes: Briefly, the model has a spatial resolution of nearly 200-km on an irregular Gaussian grid in the horizontal (corresponding to a spherical harmonic representation of model fields truncated at total wavenumber 62, T62). In the vertical, we use finite differencing of 28 levels. The model has a complete suite of physical parameterizations as described in Kanamitsu et al. (1991) with recent updates detailed in Moorthi et al. (2001). Additional updates to these parameterizations are described in Saha et al. 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. The radiation interacts with a fractional cloud cover that is diagnostically determined by the predicted cloud liquid water. Radiation also interacts with a 3 dimensional prognostic ozone that is determined from a gas-phase parameterization of ozone production and loss (McCormack et al. 2006) implemented by NCEP/EMC (Moorthi, personal communication). The 2008 experimental version of the model used for the 20th Century Reanalysis also includes the radiative effects of historical time-varying CO2 concentrations, volcanic aerosol and solar variations using the longwave radiation model of Mlawer et al. (1997) and shortwave radiation model of Hou et al. (2002). The specified boundary conditions needed to run the model in atmosphere-only mode are taken from the time-evolving sea surface temperature and sea ice concentration fields.

• Compo,G.P., J.S. Whitaker, and P.D. Sardeshmukh, 2006: Feasibility of a 100 year reanalysis using only surface pressure data. Bull. Amer. Met. Soc., 87, 175-190, doi:10.1175/BAMS-87-2-175.
• Compo, G.P., J.S. Whitaker, P.D. Sardeshmukh, N. Matsui, R.J. Allan, X. Yin, B.E. Gleaso n, 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 J. Roy. Meteorol. Soc., 137, 1-28. DOI: 10.1002/qj.776
• Shoji Hirahara, Masayoshi Ishii, and Yoshikazu Fukuda, 2014: Centennial-Scale Sea Surface Temperature Analysis and Its Uncertainty. J. Climate,27, 57-75. doi: http://dx.doi.org/10.1175/JCLI-D-12-00837.1
• Whitaker, J.S., G.P.Compo, X. Wei, and T.M. Hamill 2004: Reanalysis without radiosondes using ensemble data assimilation. Mon. Wea. Rev., 132, 1190-1200, doi:10.1175/1520-0493( 2004)132<1190:RWRUED>2.0.CO;2.
• Cram, T.A., G. P. Compo, X. Yin, R. J. Allan, C. McColl, R. S. Vose, J.S. Whitaker, N. Matsui, L. Ashcroft, R. Auchmann, P. Bessemoulin, T. Brandsma, P. Brohan, M. Brunet, J. Comeaux, R. Crouthamel, B. E. Gleason, Jr., P. Y. Groisman, H. Hersbach, P. D. Jones, T. Jonsson, S. Jourdain, G. Kelly, K. R. Knapp, A. Kruger, H. Kubota, G. Lentini, A. Lorrey, N. Lott, S. J. Lubker, J. Luterbacher, G. J. Marshall, M. Maugeri, C. J. Mock, H. Y. Mok, O. Nordli, M. J. Rodwell, T. F. Ross, D. Schuster, L. Srnec, M. A. Valente, Z. Vizi, X. L. Wang, N. Westcott, J. S. Woollen, S. J. Worley, 2015: The International Surface Pressure Databank version 2. Geoscience Data J.,2,31-46, doi:10.1002/gdj3.25. (ISPD V3.2.9)
• Giese, B. S., H. F. Seidel, G. P. Compo, and P. D. Sardeshmukh, 2015: An ensemble of historical ocean reanalyses with sparse observational input. J. Geophys. Res - Oceans, submitted. (SODAsi.2 )

Variables	Air Temperature at sigma level 0.995 (degK) Pressure at Surface (Pa) Pressure at Mean Sea Level (Pa) Precipitable Water for entire atmosphere (kg/m^2) Relative Humidity at sigma level 0.995 (%) U-wind at sigma level 0.995 (m/s) V-wind at sigma level 0.995 (m/s) (m/s)
Zonal	Global by 2.0 deg
Meridional	Global by 2.0 deg
Vertical	Surface, sigma level 0.995 and entire atmosphere
Temporal	V2: Jan 1, 1871 to Dec 31, 2012 by 6 hours V2c: Jan 1, 1851 to Dec 31, 2014 by 6 hours
Static?	no
Volume	46MB per variable per year
Server	public:
Source	http://www.esrl.noaa.gov/psd/data/gridded/data.20thC_ReanV2.html http://www.esrl.noaa.gov/psd/data/gridded/data.20thC_ReanV2c.html
Acquired	Mar 12, 2012 (Updated Nov 2016)
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