The Use of Partial Cloudiness in a Bulk Cloud Microphysics Scheme: Concept and 2D Results | CU Experts

The source and sink terms of microphysical processes vary nonlinearly with cloud condensate amount. Therefore, partial cloudiness is one of the important factors to be considered in a cloud microphysics scheme given that in-cloud condensate amount depends on the cloud fraction of the grid box. An alternative concept to represent the partial cloudiness effect on the microphysical processes of a bulk microphysics scheme is proposed. Based on the statistical relationship between cloud condensate and cloudiness, all hydrometeors in the microphysical processes are treated after converting them to in-cloud values by dividing the amount by estimated cloudiness and multiplying it after the computation of all microphysics terms. The underlying assumption is that all the microphysical processes occur in a cloudy part of the grid box. In a 2D idealized storm case, the Weather Research and Forecasting (WRF) single-moment 5-class (WSM5) microphysics scheme with the proposed approach increases the amount of snow and rain through enhanced autoconversion/accretion and increases precipitation reaching the surface.

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