Atmos. Chem. Phys. Discuss., 8, 601-686, 2008
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Modelling of cirrus clouds – Part 1: Model description and validation
P. Spichtinger1 and K. M. Gierens2
1Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland
2Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

Abstract. 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. The arctic cirrostratus case study is also supplemented with sensitivity studies including different vertical velocities, temperature fluctuations and wind shear. The model stands all tests and is thus suitable for cloud–resolving simulations of cirrus clouds. Last but not least, some new results are shown, corroborating the importance of sedimentation and dynamics inside cirrus clouds for forming the structure of the cirrus.

Citation: Spichtinger, P. and Gierens, K. M.: Modelling of cirrus clouds – Part 1: Model description and validation, Atmos. Chem. Phys. Discuss., 8, 601-686, doi:10.5194/acpd-8-601-2008, 2008.
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