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Abstract:
A proper description of the in-cloud stratification/structure and microphysics in mixed-phase clouds (MPC) is essential to improve modeled estimates of cloud shortwave cooling and longwave warming effects as well as changes in precipation in climate simulations. Even with significant progress in the understanding of primary ice formation from ice nucleating particles, the dynamics of ice multiplication from pre-existing ice particles or secondary ice production (SIP) remains a challenge in atmospheric modelling. Ice multiplication factors can reach up to four order of magnitude. SIP can accelerate ice aggregation processes leading to rapid cloud glaciation, precipitation and finally to cloud dissipation. Cloud schemes in atmospheric models just consider the Hallet-Mossop or rime-splintering mechanism, although there are SIP parametrizations via fragmentation during drop freezing or after ice-ice collisions. Recent modelling studies have addressed this issue and shown that estimates from different parameterizations differ by orders of magnitude even when functions show similar variable dependencies. It is particularly difficult to distinguish which SIP mechanism occurs in a grid point of a model domain since variable dependencies overlap among parameterizations.We worked with UCLALES-SALSA, a state-of-the-art large eddy simulation model, for a realistic representation of aerosol-hydrometeor interactions in turbulent conditions to account for SIP via rime splintering, frozen drop fragmentation, and breakup fracture after ice-ice collision. The model is used to simulate an Artic MPC case observed during the Ny-Ålesund Aerosol Cloud Experiment (NASCENT). In-cloud microphysical properties allowed us to constrain model parameters and define ranges of action for SIP mechanisms.
