ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-7-3771-2007 Physical controls on orographic cirrus inhomogeneity Kay J. E. 1 Baker M. 2 Hegg D. 2 National Center for Atmospheric Research, Boulder, CO, USA Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA 23 07 2007 7 14 3771 3781 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/7/3771/2007/acp-7-3771-2007.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/7/3771/2007/acp-7-3771-2007.pdf

Optical depth distributions (P(σ)) are a useful measure of radiatively important cirrus (Ci) inhomogeneity. Yet, the relationship between P(σ) and underlying cloud physical processes remains unclear. In this study, we investigate the influence of homogeneous and heterogeneous freezing processes, ice particle growth and fallout, and mesoscale vertical velocity fluctuations on P(σ) shape during an orographic Ci event. We evaluate Lagrangian Ci evolution along kinematic trajectories from a mesoscale weather model (MM5) using an adiabatic parcel model with binned ice microphysics. Although the presence of ice nuclei increased model cloud cover, our results highlight the importance of homogeneous freezing and mesoscale vertical velocity variability in controlling Ci P(σ) shape along realistic upper tropospheric trajectories.

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