Environmental Science and Engineering Seminar
Supercooling super-droplets: on particle-based modelling of immersion freezing
Particle-based models offer an alternative to bulk or bin (sectional) approaches for representing cloud microphysics in frameworks such as large-eddy simulations. The particle-based component of such simulations resolves the dynamics of so-called super-particles, each representing a multiplicity of modeled cloud condensation nuclei (CCN), ice nucleating particles (INP), water drops or ice particles. It is a Monte-Carlo type approach enabling detailed representation of cloud droplet and ice crystal formation and growth, and the coupling of these processes with the budget of ambient aerosol and with the flow dynamics. In this work, we focus on the representation of the immersion freezing of supercooled droplets - the ice formation process contingent on the presence of insoluble ice nuclei within the droplets. We compare two formulations based on the so-called singular and time-dependent approaches, both cast in the framework of probabilistic particle-based simulation. The comparison is carried out using an idealized two-dimensional prescribed-flow framework mimicking a stratiform mixed-phase cloud. We further explore ways of informing the particle-based model with laboratory data from immersion freezing experiments.