PROM–IMPRINT: Understanding Ice Microphysical Processes by combining multi-frequency and spectral Radar polarImetry aNd super-parTicle modelling

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Polarimetric radar observations provide rich and detailed information about the microphysics of clouds and precipitation. Using this data is challenging, though, due to the complication of the measured signals by the myriad of possible ice particle shapes and sizes. Disentangling this conundrum is the goal of this proposal. To achieve this goal state-of-the art polarimetric radar data is collected in a dedicated field campaigne targeting wintertime stratiform mixed-phase clouds. Through the combination of multi-frequency and spectral polarimetry, with the latter providing polarimetric information as a quasi-size resolved function of Doppler velocity, these measurements give us an unprecedented level of information. The richness of this data will allow to develop empirical hypotheses regarding the dominant micophysical processes in certain regions of the cloud. Such empirical hypotheses are sometimes called polarimetric fingerprints or signatures, and here we emphasize that especially for mixed-phase clouds the understanding of these polarimetric fingerprints is still uncertain, i.e., alternativ interpretations are possible. To refine and quantify these hypotheses and to develop an in-depth understanding state-of-the-art Monte-Carlo Lagrangian particle modeling is applied. Through a hierarchy of models starting from the 3d mesoscale limited-area model ICON with bulk microphysic down to a 1d spectrally-resolved Monte-Carlo process model, the observed cases will be simulated with the goal to interpret and understand the measurements. The chain of hypothesis testing does also work in the other direction. Alternative model formulations can be critically tested against the polarimetric radar observations to validate or falsify certain assumptions in the model. To bridge the gap between models and observations a reliable forward operator is needed and developed as part of the proposal. This includes new scattering calculations, e.g. for partially rimed aggregates. Through this powerful combination of advanced observing and modeling techniques with a consistent forward operator, microphysical processes like depositional growth, aggregation, riming, and ice multiplication will be investigated and our current knowledge of these processes will be put to the test. Based on this understanding of the microphysical processes the ability of the two-moment bulk microphysical model to simulate the corresponding polarimetric fingerprints will be reviewed and improved. Such improvements of the bulk process parameterizations will become possible through the unique combination of observations and process modelling, which will provide us with an almost complete knowledge of the detailed microphysical structure even in mixed-phase clouds. The ability of the two-moment bulk microphysical model to properly simulate polarimetric observations is the pre-requisite for the assimilation of such data in numericalweather prediction models or regional reanalysis.