Physical controls on orographic cirrus inhomogeneity J. E. Kay1, M. Baker2, and D. Hegg2 1National Center for Atmospheric Research, Boulder, CO, USA 2Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA
Abstract. 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.
Citation: Kay, J. E., Baker, M., and Hegg, D.: Physical controls on orographic cirrus inhomogeneity, Atmos. Chem. Phys., 7, 3771-3781, doi:10.5194/acp-7-3771-2007, 2007.