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According to the recent IPCC assessment report, the indirect impact of atmospheric aerosols remains one of the most uncertain aspects of the climate change. For shallow clouds, such as subtropical stratocumulus and trade-wind cumulus, the impact is relatively well understood at the process level. For deep clouds, on the other hand, such understanding is still missing. This is most likely because of the complexities of ice processes and because there are many forms of deep precipitating convection, from relatively small single-cell storms to mesoscale convective systems. Since a significant fraction (perhaps most) of the precipitation in the tropics and over subtropical continents originates from mesoscale convection, understanding indirect aerosol effects in such systems is an important issue. This paper will present results from a set of simulations using a two-dimensional prescribed-flow (kinematic) model mimicking the flow within a squall line combined with a comprehensive two-moment bulk warm-rain and ice scheme of Morrison and Grabowski. With the kinematic model, a large set of model simulations can be performed at a modest computational cost and the dynamic effects can be separated from those arising from cloud microphysics. The goal is to understand interactions between various microphysical processes and how these are modified by changes of the strength of convective and stratiform circulations and by the input sounding. |
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