Modelling of cirrus clouds - Part 1b: Structuring cirrus clouds by dynamics

Abstract

A recently developed and validated bulk microphysics scheme formodelling cirrus clouds (Spichtinger and Gierens, 2009), implementedinto the anelastic non-hydrostatic model EULAG is used for investigationof the impact of dynamics on the evolution of an arctic cirrostratus.Sensitivity studies are performed, using variation of large-scaleupdraughts as well as addition of small-scale temperature fluctuationsand wind shear. The results show the importance of sedimentation of icecrystals on cloud evolution. Due to non-linear processes likehomogeneous nucleation situations can arise where small changes in theouter parameters have large effects on the resulting cloud structure.In-cloud ice supersaturation is a common feature of all our simulations,and we show that dynamics is as least as important for its appearancethan is microphysics.