[Zurück]

H. Grothe, B. G. Pummer, A. Kasper-Giebl, P. Spichtinger, M. Krämer, V. Phillips:
"Final Report of the MicroDICE workshop: Atmospheric Ice Nucleation";
Bericht für European Science Foundation; Berichts-Nr. 1, 2013; 58 S.

The development of a detailed understanding of ice clouds in the atmosphere relies on the combined use of field studies, modelling at a multitude of scales, and laboratory studies that provide the necessary fundamentals. Atmospheric ice is studied by remote sensing methods from the ground, and from airplanes and satellites, using passive spectroscopic and light-scattering methods and active methods such as radar and lidar. In the Troposphere, and also, with greater difficulty, in the Stratosphere, ice is studied in situ by using airborne platforms: aircraft and balloons. In situ measurements in the mesopause region are achieved with rocket-borne instrumentation and are limited to brief sampling times as the rockets ascend and descend through cloud layers. These various methods typically lack sufficient access to fundamental physicochemical parameters of ice particles. Furthermore, the representativeness of these types of studies is always an issue because of the transient character of the involved atmospheric processes. Off-line analysis of collected samples may clarify some aspects, but usually fails for metastable particles or when aging processes are important. In these cases laboratory studies may help. Selected experiments can be performed under well controlled conditions to achieve deeper understanding of underlying processes, e.g. nucleation. Furthermore, under these controlled conditions the impact of individual parameters on the ice formation process can be determined. Theoretical and numerical models are then required to transfer the knowledge of laboratory and field studies into large-scale models using sensible parameterizations. Ice cloud nucleation is currently insufficiently understood. Ice Clouds form by different mechanisms from water vapour or liquid droplets. In many cases the ice particles cannot form from water alone. Instead some aerosol particles are known to provide surfaces on which the nucleation process is catalysed. These aerosol particles are omnipresent in the atmosphere and can act as ice nuclei, i.e. they help to reduce the height of the nucleation barrier forming stable ice crystals. Many different kinds of aerosol exist, and even individual particles vary strongly. Additionally, most atmospheric particles are internally mixed. The impacts of the aerosol nature on ice nucleation efficiency, ice microstructure and dynamics are one of the least understood parameters in cloud microphysics. The knowledge of chemists, biologists and crystallographers about the aerosol composition has to be combined with the ice dynamic models of physicists, meteorologists and computational modellers to gain a better understanding of the whole process. Only then the global impact of microstructure and dynamics of ice on e.g. the water cycle or the radiation budget can be determined accurately. The ESF research networking programme on the Micro-Dynamics of Ice has provided an ideal platform for such an intersection between the different communities and provided the capability to bring together scientists from the different fields of ice research.

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