ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-685-2009 Modelling of cirrus clouds – Part 1a: Model description and validation Spichtinger P. 1 Gierens K. M. 2 Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany 28 01 2009 9 2 685 706 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.net/9/685/2009/acp-9-685-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/685/2009/acp-9-685-2009.pdf

A double-moment bulk microphysics scheme for modelling cirrus clouds including explicit impact of aerosols on different types of nucleation mechanism is described. Process rates are formulated in terms of generalised moments of the underlying a priori size distributions in order to allow simple switching between various distribution types. The scheme has been implemented into a simple box model and into the anelastic non-hydrostatic model EULAG. The new microphysics is validated against simulations with detailed microphysics for idealised process studies and for a well documented case of arctic cirrostratus. Additionally, the formation of ice crystals with realistic background aerosol concentration is modelled and the effect of ambient pressure on homogeneous nucleation is investigated in the box model. <br><br> The model stands all tests and is thus suitable for cloud-resolving simulations of cirrus clouds.

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