1.Institute of Atmospheric Physics,Chinese Academy of Sciences;2.Yunnan Institute of Meteorological Sciences;3.Yunnan Weather Modification Center
摘 要 冰雹形成的微物理机理是人工防雹的重要科学依据，但对我国西南地区冰雹形成的微物理机理研究很少。利用中国科学院大气物理研究所三维冰雹分档云模式对云南2016年7月11日一次冰雹云过程进行了数值模拟研究，揭示了冰雹形成的微物理机制。此次冰雹云生成发展快，强度大，是西南山区典型夏季冰雹云。数值模拟的降水、降雹和回波强度等物理量与对应的观测量基本一致。模拟的冰雹云的最大上升气流速度达到28.5 ms-1。通过对冰雹形成的微物理过程分析表明，雹/霰胚的主要来源是通过过冷雨滴的概率冻结产生的冻滴，占97.8%，而冰晶碰冻雨滴产生的雹/霰胚仅占2.2%，这与国外和我国其他地区雹/霰胚产生的来源和冻滴所占比例有明显差别；形成的雹/霰胚直径多数集中在0.5mm至1.0mm范围，雹/霰胚主要通过对过冷云水的碰并过程实现增长，直径小于0.5mm的雹/霰胚较难增长，而直径大于1.0mm的雹/霰胚易于增长，大雨滴冻结成较大直径的雹胚，可促成短时间内形成冰雹；在雹云发展过程中存在短时的过冷水累积带，但过冷水累积带对雹/霰胚的增长贡献不大；对纬向风速的“零线”和冰雹增长的“穴道”区位置与变化分析提出，在雹云生长早期，应以雹云强中心顶部为防雹作业部位，随着雹云的增强发展，应以雹云强中心为防雹作业部位。
Abstract The microphysical formation mechanism of hailstones is the scientific basis of hail suppression operation, however, the relevant study on hail formation in southwestern China is few. A hail cloud case on 11 July 2016 in Yunnan is numerically simulated and studied by 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 hailstone is investigated. This hail cloud has a rapid development and high intensity, which is a typical summer hail cloud in the southwest mountainous area. The simulated rainfall, hailfall and reflectivity are generally consistent with the corresponding observations. The simulated maximum updraft velocity is 28.5 m/s. The analysis of the microphysical process of hail formation shows that the main source of hail/graupel embryos is produced by the probability freezing process of supercooled rain drops, which is accounted for 97.8%, whereas the collision between ice crystals and supercooled rain drops is only accounted for 2.2%, and the results are significantly different from the source of hail/ graupel embryos and the proportion of frozen droplets obtained in other regions in both China and other countries. The diameters of the hail/graupel embryos are mainly ranging from 0.5-1.0 mm. The growth of hail/graupel embryos depends on the collision process with the supercooled cloud water, in which, the embryos with diameter less than 0.5 mm is hard to grow, and those with diameter larger than 1.0 mm grows easily. Larger raindrops can directly freeze into larger hail embryos, which can contribute to the formation of hail in a short period of time. The short-lived accumulation zone of supercooled water occurred during the development process of the hail cloud has less contribution to the growth of hail/graupel embryos. The location and evolution of the zonal wind velocity "zero line" and hail formation “channel area” suggest that hail cloud should be suppressed at the top of the strong center in the early stage of hail clouds, and at the strong center in the hail developing and strengthening stage.