Physically based two-moment bulkwater parametrization for warm-cloud microphysics

A two-moment bulkwater parametrization scheme for warm-cloud microphysics is developed via statistical analyses of results from a detailed parcel model. This computationally efficient scheme is quite accurate and produces bulkwater properties which resemble the results from a fully explicit microphysical model. It responds sensitively to the effect of aerosol types on the cloud drop number concentration and the timing of rain initiation. Diagnostic formulae are also provided for the group fall velocity, number and mass sedimentation fluxes, the radar reflectivity factor, and the effective radii of cloud drops and raindrops. This physically sound and easy to use parametrization scheme could be useful in improving the microphysical representation in regional- and cloud-scale models.