一次降雹过程的AgI系列催化模拟研究

云数值模拟是研究降雹过程和人工防雹试验的重要手段。利用三维冰雹云AgI催化模式，对北京1996年6月10日的一次降雹过程进行AgI不同催化高度、催化剂量和催化时间的系列催化模拟试验，并优选催化方案，为外场防雹设计和作业提供依据。在催化系列模拟中发现，不同催化高度的催化剂均在上升到-5℃高度后开始核化。在2.1~4.9 km高度范围内催化，AgI成核率比较高，防雹效果较好。核化的人工冰晶有效弥补了该高度上自然冰晶的不足。小剂量催化，可在减雹的同时增加部分降雨量，而大剂量催化，在减雹的同时会减少降雨。在催化时间、剂量和高度的系列催化试验中得出，采用在模拟的第15分钟在5 km高度附近播撒AgI，连续4次以5×106 kg-1的催化剂量进行催化，催化效果较好，可减少降雹量约60%，同时可避免降雨量的大幅减少。

Numerical Modeling of Hailstorms with AgI Seeding

Cloud numerical simulations are important ways in research of hail processes and hail suppression activities. A 3-D hail model is used to simulate a hailfall case in Beijing on 10 Jun 1996. Series silver iodide (AgI) seeding simulations are designed on seeding height levels, seeding rates and starting seeding times, to get a best seeding scheme which can be used to advise outfield hail suppression operations. The 3-D hail model calculates 27 microphysical processes, which includes condensation, deposition, evaporation, collection, ice nucleation, ice multiplication, melting and freezing, auto conversions of cloud to rain, ice to graupel and graupel to hail. Seeding code is based on cloud chamber results of the mechanism of ice-forming processes by AgI which can be identified as deposition, contact freezing, condensation freezing and immersion freezing nucleation. The total nucleation activities are the sum of contributions from different nucleation modes. Humidity, temperature, cloud droplets concentration and cloud holding time are the main influence factors in AgI nucleation processes. The horizontal domain of the model is 96 km by 96 km with a constant grid increment of 1.2 km, and vertical resolution is 700 m and 20 km high. The time step is 2 s, and sounding data at 0800 BT are used as the initial.In all seeding simulations of different height levels, AgI particles start to nucleate only when they are moved to regions where air temperature is lower than-5℃. If seeding within 2.1-4.9 km height, much more ice nucleation happens, thus resulting in good hail suppression effect. The artificial ice particles make up insufficient natural ice particles. The seeding effect greatly depends on seeding amount. When the amount is less than 5×105 kg-1, hail precipitation is suppressed and rainfall is enhanced. When the amount is bigger than 1×107 kg-1, hail processes are greatly reduced and the rain processes also are weakened. For distributions of updrafts and cloud water, seeding at 12th, 15th, and 18th min, more ice nucleus is nucleated, which makes more graupel particles and better hail suppression effects than other seeding time tests. Among the series of seeding experiments, the best scheme is seeding with 5×106 kg-1 near 5 km height, at the 15th min of simulation, when hail precipitation is decreased about 60% and no much rainfall is lost.