Solar radiative forcing of mixed-phase boundary layer clouds in the Arctic

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This project is embebbed in an international effort to study climate effects of aerosols and clouds in the Arctic (VALHALA). The specific goals of the project suggested here are to evaluate the influence on the ice phase of Arctic boundary layer mixed-phase clouds on their radiative properties, and to quantify the spectral solar radiative forcing of this type of clouds. These topics have only poorly been studied in the past, although their importance for the climate system is well recognized. To reach these goals a combination of airborne radiation measurements and sophisticated single scattering an 1-D/3-D radiative transfer calculations is suggested, both in close collaboration with the partners of VALHALA. The measurements include down- and upwelling spectral irradiances with a unique instrument - the so-called albedometer. To interpret the data radiation calculations will be performed on the basis of the mixed-phase cloud microphysical properties and the spectral surface albedo determined over the Arctis ice/snow or sea surfaces. On the basis of closure between measured and calculated radiation the radiative forcing of mixed-phase clouds will be calculated.