暖底对流云催化的微物理和动力效应的数值模拟

为加深理解暖云底对流云降水形成的微物理机制,调查对这类对流云实施碘化银催化所能产生的微物理和动力效应,本文使用三维对流云模式(包含6种水成物:云滴、雨滴、冰晶、雪花、霰和冰雹),对2004年7月8日发生在我国江淮地区的一例对流云进行模拟,并开展碘化银催化试验。结果表明:(1)模式能够较好地模拟出实测风暴的回波结构。(2)云雨自动转化和霰粒子融化是两个最重要的成雨机制,产生的雨滴占雨滴总数量(质量)的67%(19%)和18%(57%)。(3)对流发展初期在主上升气流区进行的催化试验表明,对本例对流云播撒碘化银能够同时获得增雨和减雹的正效果。(4)催化增加的霰粒子通过竞争机制抑制了前期冰雹的形成,但增强了向雨滴的转化(通过融化机制);催化也促进了二次对流的发展,增加了入云的水汽通量和云水含量,加强了后期的云雨自动转化及碰并增长,导致后期的雨和冰雹增加,并使地面降水分布发生变化。这些结果表明,对暖底对流云进行碘化银催化能够产生微物理和动力效应。

Modeling the Microphysical and Dynamical Effects of Silver Iodide Seeding of Warm-Based Convective Clouds

A three-dimensional convective cloud model was used to simulate the impact of silver iodide(AgI) seeding on a subtropical convective storm that occurred on 8 July 2004 in Anhui Province, eastern China.The primary goal was to further understand the microphysical mechanisms of precipitation formation in warm-based convective clouds, and to investigate the microphysical and dynamical effects of AgI seeding.The characteristic structure of the observed storm was reproduced well by the simulation.Autoconversion of cloud water to rain and melting of graupel were the major sources of raindrops, contributing 67%(19%) and 18%(57%) of total raindrop number(mass) concentration, respectively. AgI seeding carried out in the early stages of clouds in the main updraft regions resulted in substantial increases in rain and decreases in hail.The seeding increased graupel mass and thereby inhibited hail formation in the early stages, but enhanced rain formation and growth.The seeding also enhanced secondary convection and caused the cloud to process more water vapor and thereby cloud water, leading to increases in both the autoconversion of cloud water to rain water and accretional growth of cloud water by rain and hail and, ultimately, rain and hail enhancement in the later stages. Furthermore, seeding resulted in a redistribution of precipitation on the ground.These results indicate that AgI seeding could significantly influence the cloud microphysics, dynamics and, subsequently, the precipitation of warm-based convective clouds.