The Spectral Ice Habit Prediction System (SHIPS). Part II: Simulation of nucleation and depositional growth of polycrystals

This paper proposes a framework to predict polycrystals along with hexagonal monocrystals in a cloud-resolving model and discusses validity of the scheme and physical processes important for habit distribution by implementing 2D cloud-resolving simulations of an orographic winter storm. The vapor depositional growth is simulated based on a habit frequency map constructed in the laboratory and based on a predicted growth history under evolving atmospheric conditions. Differences brought by predicting polycrystals in spatial distribution were apparent, and sedimentation of polycrystals from middle and upper levels was significant. The immersion freezing process appeared to be a key process resulting in the creation of planar polycrystals, while the homogeneous freezing process was found important for columnar and irregular polycrystals. The ice nuclei (IN) concentration was shown to affect habit distribution by changing the supersaturation, tendency of the freezing nucleation processes, and sedimentation. Preliminary comparison of simulated habit distributions and frequencies with observations indicates usefulness of the framework for polycrystals. Implications of these modeling studies on the needs of future observational campaigns are discussed.