| 过冷雨水低含量条件下冰雹形成和增长机制及其催化效果的数值模拟 |
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| 引用本文： | 陈宝君,肖辉.过冷雨水低含量条件下冰雹形成和增长机制及其催化效果的数值模拟[J].大气科学,2007,31(2):273-290. |
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| 作者姓名： | 陈宝君 肖辉 |
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| 作者单位： | 1.南京大学中尺度灾害性天气教育部重点实验室,南京大学大气科学系,南京,210093 |
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| 基金项目： | 南京大学人才培养基金资助项目和江苏省自然科学基金项目BK2004090 |
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| 摘 要： | 利用中国科学院大气物理研究所开发的三维全弹性冰雹云模式，对美国对流降水协作试验（CCOPE）期间观测的1981年8月1日雹云进行模拟，讨论在过冷雨水低含量条件下冰雹形成和增长机制及其碘化银催化效果。结果表明:(1) 自然云的模拟与观测事实一致，如最大上升气流速度、云顶高度、流场结构以及雹胚组成等。(2) 雹胚以霰为主，霰主要来自冰雪晶与过冷小水滴的碰冻，其次来自雪的积聚转化；霰、冻滴和冰雹在形成后主要靠碰并过冷云水增长。(3)人工催化试验表明，碘化银主要以凝华核（包括凝结－冻结）的作用产生大量的人工冰晶，加速了过冷水向冰晶的转化，过冷云水因而大量减少；催化后霰和冻滴的数浓度增大，对过冷云水的竞争增强，其平均尺度减小导致转化成雹的数量减少；冰雹碰冻过冷云水的增长在催化后也被削弱，导致冰雹总质量进一步减少。此外，催化后降雨量也显著减少。
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| 关 键 词： | 冰雹云 雹胚 过冷水 碘化银 CCOPE |
| 文章编号： | 1006-9895（2007）02-0273-18 |
| 修稿时间： | 2005-08-122006-04-10 |
Numerical Simulation of Hail Formation and Growth in a Storm with Low Supercooled Rain Water Content and the Effect of AgI Seeding on Hail Suppression |
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| CHEN Bao-Jun and XIAO Hui.Numerical Simulation of Hail Formation and Growth in a Storm with Low Supercooled Rain Water Content and the Effect of AgI Seeding on Hail Suppression[J].Chinese Journal of Atmospheric Sciences,2007,31(2):273-290. |
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| Authors: | CHEN Bao-Jun and XIAO Hui |
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| Institution: | 1 Key Laboratory of Mesoscale Severe Weather of Ministry of Education, Department of Atmospheric Sciences, Nanjing University, Nanjing 210093; 2 Laboratory of Cloud-Precipitation Physics and Severe Storms, Institute of Atmospheric Physics, Chinese Academy of Sci ences, Beijing 100029 |
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| Abstract: | The 1 August 1981 CCOPE (Cooperative Convective Precipitation Experiment) storm is simulated using a three-dimensional compressible nonhydrostatic cloud model with two-moment bulk microphysical parameterization to investigate the mechanism of hail formation and growth and the effect of AgI seeding on hail suppression under low supercooled liquid water content conditions. The model microphysics has 2 liquid hydrometer categories (cloud droplets and rain) and 5 ice categories that are cloud ice, snow, graupel, frozen drops and hail. Frozen drops are formed by the probabilistic freezing of rain particles, and/or contact freezing resulting from collisions of rain with cloud ice crystals or active AgI particles only when the raindrop diameter is greater than 1 mm. If the raindrop diameter is smaller than 1 mm, frozen raindrops are converted to graupel. Results show that the observed storm features, such as the maximum updraft, cloud top height, radar echoes and flow structure, and liquid water content can be better simulated. Modeling results show that the maximum supercooled cloud water content and rain water content are both about 4.4 g/m3, and 29% of the hailstone embryos are frozen drops, 71% graupel. The dominant formation mechanism for graupel is contact freezing resulting from collisions of rain with cloud ice crystals or with snow flakes and autoconversion (aggregation) of snow. Once formed, accretion of cloud water becomes the dominant growth mechanism for frozen drops, graupel and hailstone. Silver iodide is inserted into cloud at 10 min, 13 min and 16 min, respectively, to compare the effects of seeding time. Seeding location is in the core of the maximum updraft, supercooled liquid water and hail water, respectively. Seeding results in substantial decreases in hail fallout, hail impact energy and rain fallout for all seeded runs. The earlier the seeding time, the less the hail. Seeding produces significant effects, resulting in more cloud ice, more graupel but fewer cloud water. These numerous smaller hailstone embryos compete beneficially for the less available supercooled cloud water resulting in fewer hailstones than the unseeded run. Accretion of cloud water by hailstones is decreased after seeding, resulting in hail amount decrease. The rain from melting of hailstones is decreased. Although more embryos are increased by seeding, the average diameter become smaller, the rain from melting of embryos is decreased. |
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| Keywords: | hailstorm hailstone embryos supercooled liquid water silver iodide CCOPE |
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