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

Abstract

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 U.S. 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 its effectiveness for 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.

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Affiliated Institutions

• NOAA Pacific Marine Environmental Laboratory US
• Texas A&M University US
• Institute of Atmospheric Sciences and Climate IT
• University of Milan IT
• The University of Melbourne AU
• Hokkaido University JP
• National Oceanography Centre GB
• NSF National Center for Atmospheric Research US
• Lamont-Doherty Earth Observatory US
• Universitat Rovira i Virgili ES
• Physical Sciences (United States) US
• National Research Council IT
• Australian National University AU
• University of Toronto CA
• Hong Kong Observatory HK
• Cooperative Institute for Research in Environmental Sciences US
• Deutscher Wetterdienst DE
• NOAA Earth System Research Laboratory US
• University of Reading GB
• University of Colorado Boulder US
• Oeschger Centre for Climate Change Research CH
• University of Lisbon PT
• Environment and Climate Change Canada CA
• Met Office GB
• University of Southern Queensland AU
• Météo-France FR
• University of East Anglia GB
• Justus-Liebig-Universität Gießen DE
• University of Cape Town ZA
• University of Bern CH
• Columbia University US
• Riverside Technology (United States) US
• McGill University CA
• Nicolaus Copernicus University PL
• University of South Carolina US
• National Institute of Water and Atmospheric Research NZ
• Instituto Pirenaico de Ecología ES
• NOAA National Centers for Environmental Information US
• International Rescue Committee US
• National Centre for Atmospheric Science GB
• ARC Centre of Excellence for Climate System Science AU

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