Impact of Drizzle-Sized Cloud Particles on Production of Precipitation in Hailstorms: A Sensitivity Study

Abstract

This sensitivity study examined the impact of drizzle on hailstorm characteristics and precipitation on the ground. A cloud-resolving mesoscale model with a two-moment bulk microphysical scheme is modified by introducing mixing ratio and number concentration of drizzle. Therefore, the cloud model integrates the mixing ratio and number concentration of the eight microphysical particles: cloud droplets, drizzle, raindrops, cloud ice, snowflakes, graupel, frozen raindrops and hailstones. We compared two microphysical schemes depending on whether drizzle particles are present or not. It can be noted that the presence of drizzle category slows the development of the rain in the hailstorm and its appearance on the ground. The increased values of radar reflectivity factor in simulations with drizzle are a result of significantly higher values of raindrop number concentration rather than their sizes and indicate the presence of hail as well. There are prominent decreases of the radar reflectivity factor in simulations with drizzle. The occurrence of heavy showers does not exist in results without drizzle. The absence of drizzle category leads to greater accumulations of rain and a wider area of downdrafts. The alternate case produces both weaker downdrafts and smaller area of downdraft cells due to a slower autoconversion of drizzle to rain and a smaller rain evaporation. A smaller amount of surface hail is expected in the non-drizzle case.