Cloud resolving simulations of Arctic stratus - Part II: Transition-season clouds

Two-dimensional simulations of transition (fall and spring) season Arctic stratus clouds (ASC) were conducted using a sophisticated cloud resolving model with bin microphysics coupled to a two-stream radiative transfer model. The impacts of temperature variation and various ice microphysical processes on the evolution of the simulated mixed-phase ASC layer are studied. Cloud layers either collapse through rapid glaciation and ice precipitation from the cloud layer or maintain a quasi-steady state. Sensitivity studies show that the stability of the mixed-phase cloud layer is dependent upon the temperature, ice concentration, and the habit of the ice crystals, In particular, cloud layer stability is shown to be most strongly dependent upon the concentration of ice forming nuclei (IFN). In addition, it is shown that ice production and sedimentation can assist the formation of a second, lower cloud layer suggesting a new mechanism of multiple-layer formation in the Arctic. (C) 1999 Elsevier Science B.V. All rights reserved.