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河南商丘一次积层混合云过程的微物理特征与人工增雨条件研究

Microphysical Properties of a Convection-Embedded Stratiform Cloud Event and Implications for Rain Enhancement Conditions in Shangqiu, Henan

  • 摘要: 利用河南东部商丘2023年5月3日一次积层混合云过程的飞机探测数据,研究分析了此次积层混合云的水平和垂直云微物理分布特征,并基于该特征,讨论了人工增雨作业条件。结果表明,此次积层混合云过程由比较弱的倾斜西风槽过境形成,大气层结比较稳定。降雨分布范围大、且不均匀,雷达回波具有典型大范围层状云回波镶嵌对流泡回波的分布特征。并且飞机主要观测时段,研究区域降雨也比较强,对于揭示积层混合云结构特征和降水形成机制具有比较好的代表性。飞机观测显示,在层状云、对流泡边缘区域,过冷水含量很低,冰粒子以原始柱状冰晶为主。但在对流泡上部的冷云区,存在大量粒径在25 μm以下的过冷云滴粒子,最大浓度达到105~106 L-1量级。过冷水含量最大值达到0.7 g m-3以上。冰粒子主要以凇附状聚合体为主,浓度量级为100~102 L-1。由于低冰粒子浓度区域的过冷水含量比较高,适合冷云人工增雨作业。但由于高过冷水含量区的温度偏高,碘化银催化剂核化率低,更适合致冷剂(液氮、干冰)催化作业。

     

    Abstract: Stratiform clouds with embedded convection are the primary targets for aircraft-based cloud seeding for rain enhancement in China. A thorough understanding of the microphysical properties in such clouds is essential not only for the scientific design of aircraft operations but also for improving the effectiveness of rain enhancement. Using aircraft observational data collected on 3 May 2023, over Shangqiu in eastern Henan Province, this study investigates the horizontal and vertical cloud microphysical characteristics of stratiform clouds with embedded convection and discusses the associated rain enhancement conditions. The results show that the cloud event formed under the passage of a weak, tilted westerly trough with relatively stable atmospheric stratification. The rainfall distribution was wide but nonhomogeneous, exhibiting the typical structure of large-scale stratiform echoes embedded with convective echoes. The aircraft measurements were conducted during a period of intense rainfall; therefore, the collected data are well-suited for examining the structural properties of stratiform clouds with embedded convection and their precipitation formation mechanisms. The observations show that the supercooled cloud water content (SLWC) was very low in the stratiform cloud regions and at the edges of convective regions, where pristine column ice crystals were dominant. In contrast, the upper, colder portions of convective regions exhibited high concentrations of supercooled cloud droplets with diameters less than 25 μm, with number concentrations of 105–106 L−1. The maximum SLWC exceeded 0.7 g kg−1. Rimed aggregates were the dominant particles in these regions, with number concentrations of 100–102 L−1. The presence of relatively high SLWC in regions with lower ice particle concentrations indicates suitable conditions for rain enhancement operations. However, because the regions of high SLWC were primarily located within convective areas at relatively high temperatures, they are not ideal for the nucleation temperature requirements of the silver iodide agent. Thus, in such cases, the use of cooling agents, such as liquid nitrogen and dry ice, would be more appropriate for effective cloud seeding.

     

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