One of the most crucial issues for predicting future climate change is the role of clouds. Clouds can warm and cool the atmosphere depending on their properties like water content, droplet size and cloud thickness. Unfortunately, our knowledge on clouds is limited and due to the insufficient representation of cloud processes in existing climate models it is difficult to predict the role of clouds in a changing climate. We want to focus on the high level clouds (cirrus clouds) consisting purely of ice crystals. These clouds cover approximately 20-30% of the Earth's surface. For cirrus clouds, a warming of the atmosphere is possible.
However, it is rather difficult to provide estimates for the radiative effect of cirrus clouds because very little is known about the life cycle of cirrus clouds. In global climate models (GCMs) usually only the formation of cirrus clouds by synoptical dynamics (e.g. uplift along warm fronts) is regarded. However, recent studies have showed that the restriction on these processes lead to an underestimation of cirrus clouds in GCMs, because the formation of cirrus clouds due to mesoscale waves has not be taken into account. Additionally, it is not clear, how aerosols, which affected seriously the formation of cirrus clouds at synoptical conditions, will contribute to the life cycle of cirrus clouds generated by waves. Therefore, we want to study the impacts of mesoscale dynamics and aerosols on the life cycle of cirrus clouds using a highly resolved model including a complete ice microphysics.
Our objectives are to improve our knowledge about cirrus clouds and to determine the impact of dynamics versus aerosols for these clouds. From these new insights we will be able to improve our existing cirrus cloud parameterisations in t he GCMs and to develop new parameterisations, which will lead to better estimates of the radiative impact of cirrus clouds on climate.
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