Impact of stochastic collisions on cloud droplet number concentration and relative dispersion during Meiyu frontal system

Abstract

To enhance the understanding of the cloud and rain microphysical characteristics in Meiyu frontal systems, we performed a detailed analysis of stochastic collision processes in Meiyu frontal precipitation clouds, using observational data collected at the Bright Summit Meteorological Station on Huangshan (118°09′E, 30°08′N). By employing stochastic collection and breakup equations, this study investigates the primary microphysical processes influencing cloud and rain microphysical properties. Key findings are as follows: Compared to periods before and after the Meiyu season, the number concentration of small cloud droplets decreases, whereas the number concentration of large cloud droplets increases within the Meiyu season, because of relatively stronger collision-coalescence. Raindrop accretion of cloud droplets dominates the stochastic collision process, gradually reducing cloud droplet number concentration, especially, number concentration of small cloud droplets. Both cloud mean diameter and standard deviation increases with the decreasing cloud droplet number concentration, and the increase of standard deviation dominates. As a result, the correlation between cloud relative dispersion and number concentration is negative in general, but fluctuates for different number concentration ranges. This study enhances the understanding of cloud and rain microphysical processes and could be helpful to the development of microphysical parameterization schemes.