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www.atmos-chem-phys-discuss.net/11/1971/2011/
doi:10.5194/acpd-11-1971-2011
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Explicit cloud-top entrainment parameterization in the global climate model ECHAM5-HAM
1Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland
2Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, 55128 Mainz, Germany
Abstract. New developments in the turbulence parameterization in the general circulation model ECHAM5-HAM are presented. They consist mainly of an explicit entrainment closure at the top of stratocumulus-capped boundary layers and the addition of an explicit contribution of the radiative divergence in the buoyancy production term. The impact of the new implementations on a single column model study and on the global scale is presented here. The parameterization has a "smoothing" effect: the abnormally high values of turbulence kinetic energy are reduced, both in the single column and in the Californian stratocumulus region. A sensitivity study with prescribed droplet concentration shows a reduction in the sensitivity of liquid water path to increasing cloud aerosol optical depth. We also study the effect of the new implementation on a Pacific cross-section. The entrainment parameterization leads to an enhanced triggering of the convective activity.
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Citation: Siegenthaler-Le Drian, C., Spichtinger, P., and Lohmann, U.: Explicit cloud-top entrainment parameterization in the global climate model ECHAM5-HAM, Atmos. Chem. Phys. Discuss., 11, 1971-2023, doi:10.5194/acpd-11-1971-2011, 2011. Bibtex EndNote Reference Manager XML
