| Summary: | Cirrus clouds play an important role in the radiation balance of the atmosphere as theycan have a warming and cooling effect. The resulting net radiation effect depends ontheir micro- and macrophysical properties such as particle size, shape, and numberconcentration. The net warming or cooling effect of clouds is still one of the biggest uncertainties, for example in climate models. For weather and climate models and remotesensing retrievals, precise knowledge of micro- and macrophysical cloud propertiesis therefore necessary. This is true in particular for Arctic cirrus clouds, where we still lack data and need better understanding. Yet, climate change affects high latitudes stronger than other regions. Thus, more knowledge about micro- and macrophysicalproperties of Arctic cirrus clouds is needed urgently. The focus of this thesis is on the retrieval of physical particle properties of Arcticice clouds. Balloon-borne in-situ measurements with concurrent lidar measurementshave been performedinKiruna in winter. The Balloon-borne IceCloud Particle Imager(B-ICI) takes images of ice particles directly inside the cloud. After recovery, the imagesare analysed to gain information about particle shape, size, area, and number concentrationand to determine the extinction coefficient. Whenever possible, concurrent lidar measurements have supplemented the balloonbornemeasurements. Due to balloon drift, there is a spatial and temporal distance betweenB-ICI and lidar. Hence, both instruments do not sample a cloud at the same timeand place. Taking into account the wind speed, it is possible to determine the time of lidarobservation at which the cloud segment probed by balloon was closest to the lidar. However, cloud homogeneity has to be assumed. The results from B-ICI are comparedto extinction coefficients and depolarization ratios obtained fromlidar measurements. Measurement results from B-ICI and lidar measurements are, despite the spatial andtemporal distance, very similar and thus comparable. Clouds consisting of small ...
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