Towards a more reliable historical reanalysis: Improvements for version 3 of the Twentieth Century Reanalysis system

Laura C. Slivinski, Gilbert P. Compo, Jeffrey S. Whitaker, Prashant D. Sardeshmukh, Benjamin S. Giese, Chesley McColl, Rob Allan, Xungang Yin, Russell Vose, Holly Titchner, John Kennedy, Lawrence J. Spencer, Linden Ashcroft, Stefan Brönnimann, Manola Brunet, Dario Camuffo, Richard Cornes, Thomas A. Cram, Richard Crouthamel, Fernando Domínguez‐CastroJ. Eric Freeman, Joëlle Gergis, Ed Hawkins, Philip D. Jones, Sylvie Jourdain, Alexey Kaplan, Hisayuki Kubota, Frank Le Blancq, Tsz‐Cheung Lee, Andrew Lorrey, Jürg Luterbacher, Maurizio Maugeri, Cary J. Mock, G. W. Kent Moore, Rajmund Przybylak, Christa Pudmenzky, Chris Reason, Victoria C. Slonosky, Cathy Smith, Birger Tinz, Blair Trewin, Maria Antónia Valente, Xiaolan L. Wang, Clive Wilkinson, Kevin Wood, Przemysław Wyszyn'ski

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Historical reanalyses that span more than a century are needed for a wide range of studies, from understanding large‐scale climate trends to diagnosing the impacts of individual historical extreme weather events. The Twentieth Century Reanalysis (20CR) Project is an effort to fill this need. It is supported by the National Oceanic and Atmospheric Administration (NOAA), the Cooperative Institute for Research in Environmental Sciences (CIRES), and the Department of Energy (DOE), and is facilitated by collaboration with the international Atmospheric Circulation Reconstructions over the Earth initiative. 20CR is the first ensemble of sub‐daily global atmospheric conditions spanning over 100 years. This provides a best estimate of the weather at any given place and time as well as an estimate of its confidence and uncertainty. While extremely useful, version 2c of this dataset (20CRv2c) has several significant issues, including inaccurate estimates of confidence and a global sea level pressure bias in the mid‐19th century. These and other issues can reduce the effectiveness of studies at many spatial and temporal scales. Therefore, the 20CR system underwent a series of developments to generate a significant new version of the reanalysis. The version 3 system (NOAA‐CIRES‐DOE 20CRv3) uses upgraded data assimilation methods including an adaptive inflation algorithm; has a newer, higher‐resolution forecast model that specifies dry air mass; and assimilates a larger set of pressure observations. These changes have improved the ensemble‐based estimates of confidence, removed spin‐up effects in the precipitation fields, and diminished the sea level pressure bias. Other improvements include more accurate representations of storm intensity, smaller errors, and large‐scale reductions in model bias. The 20CRv3 system is comprehensively reviewed, focusing on the aspects that have ameliorated issues in 20CRv2c. Despite the many improvements, some challenges remain, including a systematic bias in tropical precipitation and time‐varying biases in southern high latitude pressure fields.
Original languageEnglish
Pages (from-to)2876-2908
JournalQuarterly Journal of the Royal Meteorological Society
Issue number724
Early online date3 Jul 2019
Publication statusPublished - Oct 2019

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