PolarCAP: Remote sensing and modeling of cloud microphysical processes in thermodynamically and aerosol‐constrained super‐cooled stratus clouds

The project Polarimetric Radar Signatures of Ice Formation Pathways from Controlled Aerosol Perturbations (PolarCAP) aims at tackling the complex problem of the evolution of the ice phase at slightly supercooled conditions by means of observations in a thermodynamically and aerosolcontrolled natural environment using radar polarimetry and spectral‐bin modelling. PolarCAP is implemented in close collaboration with the external ERC research project CLOUDLAB of ETH Zurich. The targets of the study are predominantly liquid supercooled stratiform cloud layers which frequently form during wintertime in the temperature range from ‐10 to 0°C over the Swiss Plateau.The observations will build on a solid foundation of previous achievements of TROPOS and previous collaborations. Doppler peak separation and multi‐wavelength techniques, retrievals of ice‐crystal size distributions, determination of particle habits techniques, all based on scanning polarimetric cloud radar observations, will be combined with fall‐streak tracking and liquid‐water retrievals to obtain a comprehensive picture of the cloud evolution. In collaboration with CLOUDLAB, evaluation data will be obtained in‐situ with UAV and holographic ice particle imagers, which will be used to challenge the remote‐sensing‐based retrievals.Within the PolarCAP project the remote sensing equipment of LACROS (Leipzig Aerosol and Cloud Remote Observations System) is installed in Eriswil, Switzerland during three winter campaigns 2022‐ 2025. This contribution will introduce PolarCAP. We will further present first results of our cloud microphysical measurements and their evaluation against CLOUDLAB in‐situ observations, as well as associated spectral‐bin model simulations, with the focus on hydrometeor characterization and retrieval evaluation.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)