ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-11-1971-2011 Explicit cloud-top entrainment parameterization in the global climate model ECHAM5-HAM Siegenthaler-Le Drian C. 1 Spichtinger P. 2 Lohmann U. 1 Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, 55128 Mainz, Germany 20 01 2011 11 1 1971 2023 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/11/1971/2011/acpd-11-1971-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/11/1971/2011/acpd-11-1971-2011.pdf

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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