Combined Active Remote Sensing and Modeling of Ice Nucleating Particles and Ice Crystal Flux (COARSEMIX)

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Clouds occur globally and always cover more than 30% of the Earth's surface. They have, thus, a strong influence on the radiative balance of the atmosphere by permanently changing Earth's albedo. The processes driving cloud evolution are poorly understood, especially ice phase transitions via heterogeneous freezing, and thus their simplified representation in atmospheric circulation models presently motivates numerous research activities. It is a fundamental question, at what rate free-tropospheric aerosol is transported into a mixed phase cloud layer, resupplying it with cloud condensation nuclei and ice nucleating particles (INP). A detailed description of this process for elevated cloud layers (altocumulus, altostratus) on the basis of modeling and observation is absent, although elevated cloud layers are ideal for aerosol-cloud-dynamics related studies. We propose a study that will investigate aerosol entrainment and the formation of ice particles within such cloud layers, based on active remote-sensing observations (lidar/radar) and detailed numerical cloud modeling. The aerosol transport within elevated cloud layers will be studied by means of state-of-the-art numerical cloud-resolving modeling. For a simultaneous closure between the flux of INP into a cloud layer and the flux of ice crystals out of it, the models have to be capable of explicitly simulating aerosol transport and subsequent ice formation in cloud layers. Within the recent years, such numerical cloud models have been developed at TROPOS. The here proposed COARSEMIX (Combined Active Remote SEnsing and Modeling of Ice-nucleating particles and ice crystal fluX) project will be the first combined remote-sensing/modeling closure experiment for the number concentrations of INP and ice crystals. It will deliver information about the interaction between aerosols, dynamics, ice formation, cloud formation and precipitation. The project will enable direct implementation of new aerosol/ice parameterization into models, due to the close interaction between the modeling and the observational components.