Numerical Simulation on the Microphysical Formation Mechanism of a Typical Hailstorm Process in Yunnan, Southwestern China

The microphysical formation mechanism of hailstones is the scientific basis of hail suppression operation. However, the relevant study on this issue in southwestern China is few. A hailstorm case on July 11, 2016, in Yunnan is numerically simulated using the three-dimensional cloud model with hail-bin microphysics developed by the Institute of Atmospheric Physics, Chinese Academy of Sciences, and the microphysical formation mechanism of the hailstorm is investigated. The hail cloud developed rapidly with high intensity and is a typical summer hail cloud in the southwest mountainous region. The simulated physical parameters such as rainfall, hailfall, and reflectivity are generally consistent with those observed. The simulated maximum updraft is 28.5 m/s. The microphysical processes of the hailstorm indicate that the main source of hail/graupel embryos is produced by the probability freezing process of supercooled raindrops, which is accounted for 95%, whereas the source via the collision between ice crystals and supercooled raindrops is only accounted for 5%, which are significantly different from other regions in both China and other countries. The diameters of hail/graupel embryos mainly range from 0.3–3.0 mm. The growth of hail/graupel embryos depends on the collision process with the supercooled cloud water, in which the embryos with a diameter less than 0.3 mm are hard to grow. Larger raindrops can directly freeze into larger hail embryos, which can contribute to the formation of hailstones in a short period. A short-lasting accumulation zone of supercooled rainwater occurs in the development process of the hail cloud, and it has little contribution to the growth of hail/graupel embryos.