Untersuchungen zur Wasser-Partitionierung in Zirruswolken : Feldmessungen und Modellrechnungen

Cirrus clouds influence climate change. However, forming mechanisms and their influences on the development of cirrus clouds are not investigated very well. For the knowledge on climatic relevance of different types of cirrus clouds we need more information on cirrus forming and development. In situ measurements of water vapour and ice water content sampled and evaluated during this doctoral thesis will give information on the partitioning of water in cirrus clouds and will improve our understanding of cirrus development. For water vapour measurements, the state of the art instrument OJSTER (Open-path Jülich’s Stratospheric Tdl-ExpeRiment) was put into operation and run successfully during several campaigns. The measured data sets complete a unique data set of measurements in cirrus clouds. Its temerature ranges from 180 to 240 K and covers all three regions of climate — arctics, mid latitude and tropics. With ice nucleation the partitioning of water in cirrus clouds starts. Crystals form and grow due to water uptake. In the past high relative humidity with respect to ice $(RH_{i} \approx$ 200 %) was observed inside cirrus clouds. But the mechanisms making such high RH$_{i}$ possible are investigated sparcely. Using a theoretical framework invented by Korolev et al. and a new climatology, I can show the possibility to create such high RH$_{i}$ in dynamic equilibrium of the clouds due to thermodynamic processes only. The most important parameters influencing RH$_{i}$ are presented. The case study of a cirrus cloud observed during the CIRRUS 2004 campaign shows in situ measurements of RH$_{i}$, ice water content, number density, and size of ice crystals inside the ice cloud. These parameters are used to initialize modell calculations with theEULAG modell$^{1}$. That cirrus clouds’ water partitioning can be influenced by several processes where thermodynamic processes might be dominant follows from this case study