A two-moment cloud microphysics parameterization for mixed-phase clouds. Part 1: Model description

A two-moment microphysical parameterization for mixed-phase clouds was developed to improve the explicit representation of clouds and precipitation in mesoscale atmospheric models. The scheme predicts the evolution of mass as well as number densities of the five hydrometeor types cloud droplets, raindrops, cloud ice, snow and graupel. Since the number concentrations of all these hydrometeors are calculated explicitly, all relevant homogenous and heterogenous nucleation processes have been parameterized including the activation of cloud condensation nuclei, which is not predicted in most state-of-the-art cloud resolving models. Therefore the new scheme can discriminate between continental and maritime conditions and can be used for investigations of aerosol effects on the precipitation formation in mixed-phase clouds. In addition, the scheme includes turbulence effects on droplet coalescence, collisional breakup of raindrops and size-dependent collision efficiencies. A new general approximation of the collection kernels and the corresponding collision integrals is introduced.