Influence of drop size distribution function on simulated ground precipitation for different cloud droplet number concentrations

A cloud-resolving mesoscale model with a two-moment bulk microphysical scheme is used to perform cloud simulations for two different modes of the liquid water spectrum: a unified Khrgian-Mazin size distribution for the entire spectrum of drops and the monodisperse size distribution for cloud droplets with the exponential Marshall-Palmer distribution for raindrops. The cloud model calculates the mixing ratios and number concentrations of the six microphysical categories: raindrops, cloud ice, snow, graupel, frozen raindrops and hail. The cloud droplet number concentration was prescribed. The main purpose of this sensitivity study was to analyse the differences in simulated surface precipitation (rain and hail) for the two assumed approaches with different values of cloud droplet number concentration. The study showed that there are significant differences in the occurrence, amount and spatial distribution of accumulated precipitation at the surface. It can be noted that the unified Khrgian-Mazin size distribution is generally more sensitive to changes in the cloud droplet number concentration than an alternative approach. The rain showers and cloud splitting are well simulated with the unified Khrgian-Mazin size distribution, especially for smaller values of cloud droplet number concentration.