Study of the ice phase in Arctic mixed-phase clouds and its influence on the cloud-radiation interaction (EPOPEE) within the international atmospheric research project ASTAR (Arctic Study of Tropospheric Aerosol and Radiation)

The project EPOPEE is embedded in the international project ASTAR to study direct and indirect climate effects of aerosols and clouds in the Arctic. The particular goals of the project EPOPEE are to experimentally characterize the ice phase in Arctic clouds (including the ice phase) in situ, to study the aerosol-cloud as well as cloud-radiation interactions, and to develop adequate methods to validate remote sensing cloud parameters. In 2004 the project EPOPEE is mainly organized around in situ observations of detailed microphysical and optical cloud properties onboard the Polar-2 aircraft during the transition from polluted Arctic haze (observed especially in late winter, early spring months) to clean summer aerosol conditions. The transition from Arctic haze to clean summer conditions is quite sharp (a large amount of aerosols coming from Eurasian industrial areas accumulate over the Arctic and cover the Arctic by a layer of a smog-like haze of the size of the continent of Africa) due to a radical change in atmospheric transport patterns and is, thus, easy to identify. During Arctic summer, the high latitudes are then more or less “protected” from long-range transport of air masses from lower latitudes. The principal scientific objective of the project EPOPEE in 2004 will focus on studying the aerosol-cloud interactions with particular attention given to the ice phase nucleation in Arctic mixed-phase clouds. The interpretation of the instrumental observations will broadly benefit from a very close cooperation with the LaMP modelling group for theoretically coupling small-scale processes (cloud particle nucleation) with meso-scale dynamics. Furthermore, the project will focus on cloud-radiation interaction and the development of adequate methods to validate cloud parameters retrieved from remote sensing techniques. Therein, we will experimentally answer the question of how the different ice crystal shapes govern the scattering phase function of respective crystals. Moreover, the in situ cloud measurements will allow to develop an adequate strategy for the interpretation of remote sensing data from a depolarisation Lidar onboard the same aircraft (Polar-2).