Robustness and sensitivities of central U.S. summer convection in the super-parameterized CAM: Multi-model intercomparison with a new regional EOF index

Authors

  • Gabriel J. Kooperman,

    Corresponding author
    1. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
    • Corresponding author: G. J. Kooperman, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Dr., Dept. 0224, La Jolla, CA 92093-0224, USA. (gkooperman@ucsd.edu)

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  • Michael S. Pritchard,

    1. Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
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  • Richard C. J. Somerville

    1. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
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Abstract

[1] Mesoscale convective systems (MCSs) can bring up to 60% of summer rainfall to the central United States but are not simulated by most global climate models. In this study, a new empirical orthogonal function based index is developed to isolate the MCS activity, similar to that developed by Wheeler and Hendon (2004) for the Madden-Julian Oscillation. The index is applied to compactly compare three conventional- and super-parameterized (SP) versions (3.0, 3.5, and 5.0) of the National Center for Atmospheric Research Community Atmosphere Model (CAM). Results show that nocturnal, eastward propagating convection is a robust effect of super-parameterization but is sensitive to its specific implementation. MCS composites based on the index show that in SP-CAM3.5, convective MCS anomalies are unrealistically large scale and concentrated, while surface precipitation is too weak. These aspects of the MCS signal are improved in the latest version (SP-CAM5.0), which uses high-order microphysics.

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