The Canadian Fourth Generation Atmospheric Global Climate Model (CanAM4). Part I: Representation of Physical Processes

Abstract

The Canadian Centre for Climate Modelling and Analysis (CCCma) has developed the fourth generation of the Canadian Atmospheric Global Climate Model (CanAM4). The new model includes substantially modified physical parameterizations compared to its predecessor. In particular, the treatment of clouds, cloud radiative effects, and precipitation has been modified. Aerosol direct and indirect effects are calculated based on a bulk aerosol scheme. Simulation results for present-day global climate are analyzed, with a focus on cloud radiative effects and precipitation. Good overall agreement is found between climatological mean short- and longwave cloud radiative effects and observations from the Clouds and Earth's Radiant Energy System (CERES) experiment. An analysis of the responses of cloud radiative effects to variations in climate will be presented in a companion paper.

[Traduit par la rédaction] Le Centre canadien de la modélisation et de l'analyse climatique (CCmaC) a mis au point la quatrième génération du modèle canadien de circulation générale de l'atmosphère (CanAM4). Le nouveau modèle comprend des paramétrisations physiques passablement modifiées comparativement à son prédécesseur. En particulier, le traitement des nuages, des effets radiatifs des nuages et des précipitations a été modifié. Les effets directs et indirects des aérosols sont calculés à l'aide d'un schéma d'aérosols en bloc. Nous analysons des résultats de simulation pour le climat général du jour présent en mettant l'accent sur les effets radiatifs des nuages et les précipitations. Nous trouvons un bon accord général entre la moyenne climatologique des effets radiatifs des nuages pour les courtes et les grandes longueurs d'onde et les observations de l'expérience CERES (Clouds and Earth's Radiant Energy System). Une analyse de la réponse des effets radiatifs des nuages aux variations du climat sera présentée dans un article connexe.

Keywords:

• global climate model
• cloud parameterization
• convection
• radiative transfer

Acknowledgements

We thank three anonymous reviewers for helpful comments. We further thank Ulrike Lohmann, Phil Austin, Howard Barker, and co-workers for contributions to the development of cloud and aerosol parameterizations, and Steven Lambert and Slava Kharin for providing diagnostic tools and datasets. Helpful comments on the manuscript by Greg Flato and Phil Austin are acknowledged. CERES data were obtained from the NASA Langley Research Center CERES ordering tool at http://ceres.larc.nasa.gov/. ISCCP data were obtained from http://eosweb.larc.nasa.gov/PRODOCS/isccp/table_isccp.html. GPCP precipitation data were provided by the World Meteorological Organization's World Data Centre at NOAA's National Climatic Data Centre, from http://ncdc.noaa.gov/oa/wmo/wdcamet-ncdc.html. Major funding was provided by Environment Canada, the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS), the Climate Change Action Fund (CCAF), and the National Sciences and Engineering Research Council of Canada (NSERC).

Additional information

Notes on contributors

Xiaoyan Ma

†Current affiliation: The Atmospheric Sciences Research Center, State University of New York at Albany, New York, USA.