Towards Understanding the Phase Composition of Mixed-Phase Clouds in High Latitudes using a Novel Airborne Technique for Discriminating Ice Crystals and Liquid Droplets

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Mixed-phase clouds remain one of the greatest source of uncertainties in understanding the high latitude response to climate change in particular due to an inaccurate representation of the relative composition of ice and liquid phases (phase composition). Still, discrepancies exist between the modeled and measured ice particle concentrations, which leads to inaccurate representation of the cloud macrophysical properties, such as cloud fraction, and to miscalculation of the deposited solar energy. In-situ measurements are needed to address these discrepancies and to improve climate and general-circulation models. However, in high latitudes in-situ measurements are either scarce or limited by the capabilities of the in-situ instruments to discriminate the phase of small (<50 micrometer) cloud particles.The uncertainty in the phase composition and especially the existence of small ice particles in high latitude mixed-phase clouds was the motivation for this proposal. We plan to investigate the existence of small ice particles and the ice particle concentrations in upcoming field campaigns in the Arctic and in the Southern Ocean and simultaneously get a detailed insight into the microphysical and optical properties of those ice particles. To reach our goals, we propose to use the existing Particle Habit Imaging and Polar Scattering (PHIPS) probe that combines ice particle imaging and scattering measurements and develop a new data product that separates spherical droplets from aspherical ice particles based on their angular light scattering properties.The main objectives of the proposed project will be (1) the selective detection of ice particles in the sub-50 micrometer size range in high latitude mixed-phase clouds, (2) the characterization of the microphysical properties of mixed-phase cloud particles, including the ice crystal shape and crystal complexity, and (3) the quantification of the shortwave angular light scattering properties of mixed-phase ice particles. The analysis of the data gathered from three field campaigns combined with cloud chamber simulation experiments will provide an important contribution to the understanding of the high latitude response to climate change and its representation in climate models.