Comparison of bulk and bin warm rain microhpysics models using a kinematic framework

A new two-moment bulk microphysics scheme predicting the number concentrations and mixing ratios of cloud water and rain is developed and tested against a bin-resolving microphysics model using a 2D kinematic framework. This approach allows for the testing of schemes in a realistic flow field on the cloud-resolving scale without added complexities due to feedbacks with the dynamics. Two different configurations of the kinematic model are utilized, corresponding to boundary-layer stratocumulus and shallow cumulus. The bin and bulk models are run under both polluted and pristine aerosol regimes to gauge the ability of the bulk model to simulate indirect aerosol effects on cloud optical properties and precipitation rate. It is found that the bulk model is able to reasonably capture the bin model results for both the stratocumulus and cumulus regimes. Sensitivity tests show that the prediction of both rain number concentration and mixing ratio, rather than rain mixing ratio only, is critical for simulating aerosol indirect effects using the bulk model.