三维对流云催化数值模式人工冰晶参数化方案的改进与个例模拟试验

在中国科学院大气物理研究所的三维全弹性对流风暴云催化数值模式(简称为IAP-CSM3D)的基础上,对模式中催化部分的参数化方案进行了改进,推导出人工冰晶与其它粒子之间相互作用的微物理过程的参数化方程。改进后的模式将催化产生的人工冰晶单独作为预报量进行处理,把人工冰晶与自然冰晶区分开,且考虑的人工冰晶谱型为双参数粒子谱,使模式更符合实际。利用改进后的模式模拟了2005年7月8日发生在辽宁省朝阳市的一次冰雹云天气过程,着重分析了催化云人工冰晶的微物理过程、空间分布和谱型,以及对冰相降水粒子的贡献。数值试验表明,自然雹云模拟结果与观测事实相吻合,说明改进后的模式对冰雹云具有较可靠的模拟能力。模拟分析表明,冻滴是该例自然雹云冰雹胚胎的主要来源,对该冰雹云进行AgI催化可明显地减少降雹量,特别是在云中冰雹形成初期进行催化防雹效果最好,既可产生最大的防雹作业效果又不至于过度减少降雨量。催化减雹的主要原因是催化显著地减少了云中冻滴向冰雹胚胎的转化总量。进一步研究发现,人工冰晶在云的不同阶段对各种冰相降水粒子的贡献是不同的。人工冰晶对雪花总质量的贡献较小,对霰总质量的贡献有所增大,而对冻滴总质量的贡献较大。模拟的冰晶粒子谱可较好地反映出人工冰晶谱型较窄,浓度较大,尺度较小的特征。

The Improvement of Artificial Ice Crystal Parameterization of IAP Three-Dimensional Convective Storm Model and Its Application to Case Study

On the base of IAP-CSM3D(Three-Dimensional Convective Storm Model) which was set up by the Institute of Atmospheric Physics(IAP),Chinese Academy of Sciences,its parameterization of artificial seeding was improved.The parameterization equations of microphysical processes that contact with artificial ice crystals were deduced.In the ameliorated model,the artificial ice crystals induced by cloud seeding were treated as a separate predictand.Natural ice crystals and artificial ice crystals were discretely considered in the ameliorated model comparing with its former.The size distribution of artificial ice crystals was considered as a double-moment parameterization to more accord with fact.Then a hailstorm event occurred in Chifeng City in North China on 8 July 2005 was simulated by the ameliorated model to analyze the influence of artificial ice crystals on hailfall and the microphysical processes of artificial ice crystals.The results show that the model simulation is very consistent with observation,indicating the improved IAP-CSM3D model has more credible ability in seeding simulation than its former.The results of the simulation of natural cloud show that frozen drop is the main hail embryo in the simulated hailstorm.The simulations also indicate that seeding AgI in the hailstorm may markedly decrease the hailfall amount,especially in the earlier stage of hailstone formation in the seeding cloud,seeding cloud may have the best effect of reducing hail shooting,which can obtain a maximal effectiveness of reducing hail shooting,under a condition that the seeding can keep a minimal reduction in its rainfall amount.The primary cause of reducing hailfall is that seeding can remarkably abate the transformation amount of frozen drops into hail embryos in the hailstorm.There are different contributions of artificial ice crystals to ice-phase precipitation particles at different stages of cloud development.Simulations illustrate that the artificial ice crystals have little contribution to snow but more to frozen drop and graupel.The simulated result also shows characteristics that artificial ice crystals have a narrower size distribution with a smaller average size and a larger concentration.