A comprehensive two‐moment warm microphysical bulk scheme. II: 2D experiments with a non‐hydrostatic model

A new bulk microphysical scheme containing advanced parametrizations to predict both concentration and mixing ratio of cloud droplets and raindrops (see Part I) is implemented in a three-dimensional non-hydrostatic model. This paper presents results obtained with the complete scheme for two specific experiments of idealized precipitating clouds. In the first case, an orographic cloud is produced at the windward edge of a plateau. The study focuses on the sensitivity of the microphysical fields and precipitation patterns to the upwind cloud condensation nuclei (CCN) activation spectrum. In the second case, a heavily precipitating tropical rainband of the Hawaiian Rainband Project is simulated in a kinematic framework. Analysis of simulated radar-reflectivity time evolution indicates that a realistic development of large raindrops can be obtained as compared to either observations or to results produced by a bin-resolving model. The overall control of raindrop tail distribution by collisional break-up is re-emphasized in the light of earlier results. The rather simple tests lead to the conclusion that a complete bulk microphysical scheme can simulate warm rain processes with reasonable accuracy. The ability of the model to account for realistic CCN activation spectra with modest programming effort makes the scheme suitable for three-dimensional precipitation simulations that properly take into consideration aerosol dynamics at mesoscale.

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