PIs: André Ehrlich, Andreas Macke, Susanne Crewell

The representation of Arctic mixed–phase clouds in climate models is still challenging and proven to result in uncertainties in the surface and atmospheric energy budget of model simulations. These errors reduce the confidence in our ability to predict the cloud contribution to Arctic Amplification and result mostly from our lack of understanding the diversity of interaction and feedback processes connected to mixed–phase clouds. Especially, the ice phase is found to be a key parameter for the cloud life cycle and their energy budget but observational process studies on ice formation, growth, and sedimentation, are still rare.

We propose novel observation strategies for Arctic clouds by combining airborne remote sensing with insitu microphysical measurements of cloud and aerosol properties. Using two identical collocated aircraft, Polar 5 and 6, it will be possible to simultaneously measure the microphysical particle characteristics within clouds by in–situ sensors and probe the vertical column and radiative impact from remote sensing measurements above clouds. Two campaigns each with 80 flight hours will be performed in summer 2017 (ACLOUD, Svalbard) and spring 2019 (AFLUX, Svalbard and Greenland) to investigate typical Arctic boundary layer clouds as part of the major experimental activities of the TR 172.

In situ sampling of cloud and aerosol particles will be realized by a counterflow virtual impactor (CVI) which allows a comprehensive microphysical and chemical characterization of the ice nuclei (IN), cloud condensation nuclei (CCN) and ambient aerosol particles by means of different aerosol sensors. Supported by in–situ observations and remote sensing of cloud particle properties the measurements will improve our view on the heterogeneous nucleation mechanism in Arctic mixed–phase clouds. The remote sensing instrumentation will comprise passive observations of reflected spectral solar and emitted microwave radiation as well as active profiling by radar and lidar. The combination of these different techniques will allow to quantify the horizontal and vertical distribution of ice within the cloud and precipitating particles. Information on cloud liquid and ice within the column will be provided by a multi–channel microwave radiometer and imaging spectrometer while active instruments, i.e., radar and lidar, will resolve the vertical structure. The retrieved pattern of the partitioning between ice and liquid water will be linked to observed aerosol and precipitation properties and to measurement–based estimates of the cloud radiative forcing. We aim to characterize the entire life cycle of ice crystals in Arctic mixed–phase clouds, starting from ice nucleation and ending in precipitating snow, and to identify how the cloud radiative forcing will adjust to changes of the ice life cycle.

• Evaluation of Large Eddy Simulations (E03)
• MiRAC observations and data processing in close collaboration with E02
• Evaluate the representativeness of ground-based aerosol characterizetion (B04)