气溶胶对新疆冰雹形成物理过程影响的数值模拟研究

利用带有分档微物理方案的中尺度模式（WRF-SBM）模拟了一次新疆夏季的冰雹天气过程，并通过敏感性试验研究了气溶胶浓度变化对雹云微物理特征、降水过程及冰雹形成机制的影响。结果表明:初始气溶胶浓度越大，对流云发展越旺盛。雹云发展阶段，云中液水含量随气溶胶浓度增加而增多，冰水含量在中度污染时最多。冰雹的含量随气溶胶浓度的增加呈现先增加后减小的趋势，相较而言中度污染条件下，云滴尺度适当，过冷云水含量相对充足，更有利于液相水成物向冰粒子的转化，也更有利于冰雹的生长。冰雹最初几乎全部由冰晶碰冻过冷水生成，随后该过程迅速减弱，液滴冻结过程短暂地成为主要来源，但冰雹一旦形成，自身就会迅速收集过冷水开始生长，成为冰雹生长的主导过程。重度污染条件导致各种成雹过程推迟发生。气溶胶浓度增大导致地面液相累积降水增加，冰相累积降水先增加减少，并且气溶胶浓度适当增大可使降雹量及冰相降水中冰雹的比重增加，过量则会减小。在此基础上，本文提出最适合冰雹生长的“最优气溶胶浓度”，同时也是人工防雹工作中应重点关注的浓度。

Numerical Simulation of Aerosol Effects on the Physical Processes of Hail Formation in Xinjiang

The weather research and forecasting model with a spectral-bin microphysical scheme (WRF-SBM) was used to simulate a hailstorm that occurred in Xinjiang during a summer. The effects of aerosol concentration on the microphysical characteristics and precipitation of the hailstorm and hail formation mechanism were studied via sensitivity tests. The results show that the convection of the hailstorm increases in strength with increasing aerosol concentration. At the development stage of the hailstorm, the liquid water content increases with increasing aerosol concentration, and the ice water content is the highest under moderate pollution conditions. With the increase in aerosol concentration, the hail mixing ratio first increases and then decreases. Under moderate pollution conditions, the cloud droplet size is appropriate, and the amount of supercooled water is relatively sufficient, which are favorable conditions for the transformation of water from the liquid to ice phase, thus contributing to hail growth. Hail is initially formed by the riming of supercooled liquid water by ice crystals, but this process is rapidly weakened after the hailstorm development. Further, the freezing of droplets becomes the main source of hail formation for a short while. However, once the hails are formed, they grow rapidly by collecting the supercooled water, which becomes the dominant process of the hail growth. The severe pollution condition will delay the start of hail formation processes. With enhanced aerosol loading, the surface accumulated liquid precipitation increases, whereas, the ice-phase precipitation first increases and then reduces. The moderate aerosol concentration leads to a large amount of hail mixing ratio and a high percentage of hail in the ice-phase precipitation. However, with further increase in aerosol concentration, both values are reduced. Therefore, we propose “optimal aerosol concentration,” which is the most suitable condition for hail growth.