A two-moment bulk microphysical parameterization of snow, graupel and hail with explicit liquid water fraction

Common bulk microphysical parameterizations of precipitation-sized ice particles, i.e. snow, graupel and hail, make strong simplifications when it comes to the processes of formation, growth and melting. Focusing on the melting process, these simplifications can lead to significant problems and biases in simulations of the melting layer and the amount and phase of particles reaching the ground. For instance, a proper representation of melting ice particles is needed for the simulation of convective cold pools, the organization of deep convection, and for a quantitative validation with remote-sensing observations. Especially for very high-resolution simulations of deep convection, a microphysics scheme which allows for internally mixed particles with explicit liquid water fraction would be appropriate or even necessary.

We will introduce a framework for a parameterization representing the ice particles' liquid water fraction and the methodology for the formulation of the closure equations for snow, graupel and hail in a two-moment bulk scheme. Results using a one-dimensional column model with bin microphysics to investigate the bulk properties of melting ice particles on a process level will be presented. Furthermore, we hope to present first results of a deep convective test case simulation with the UCLA-LES model using the extended parameterization. This project is part of the German research program 'High-definition clouds and precipitation for advancing climate prediction', which aims at the large-eddy simulation of clouds and deep convection on the meso-alpha-scale.