Modeling of cloud microphysics: from simple concepts to sophisticated parameterizations
Wojtek Grabowski, National Center for Atmospheric Research (NCAR) Boulder, Colorado

This lecture will review physical processes resulting in growth of water droplets and ice crystals in clouds (commonly referred to as cloud microphysics),  and present various approaches to model them. We will start with simple approaches resulting from the assumption of thermodynamic equilibrium. For ice-free clouds, such an approach leads to a fairly simple system of coupled PDEs representing warm-rain bulk microphysics. It can be extended to ice-bearing clouds, but complexities of the ice phase make the task difficult and additional (often poorly-justified) assumptions are needed. When the thermodynamic disequilibrium is allowed, both warm-rain and ice microphysics require information about particle size distributions. For the warm-rain, nucleation of cloud droplets and their further growth by diffusion of water vapor and by gravitational collision-coalescence can be modeled using a system of several dozens of coupled PDEs (the so-called bin-microphysics). Extension of such an approach to mixed-phase clouds (droplets and ice crystals) is even more difficult.