基于飞机真实轨迹的一次层状云催化的增雨效果及其作用机制的模拟研究

Simulation of stratiform cloud seeding，its rainfall enhancement effect and mechanism study based on a real trajectory of aircraft

中文关键词:  层状云  人工增雨效果  中尺度催化模式  飞机轨迹模拟  碘化银核化  微物理链条  动力效果

英文关键词:Stratiform cloud  Rainfall enhancement effect  Mesoscale seeding model  Aircraft track simulation  AgI nucleation  Microphysical chain  Dynamic effect

中文摘要:

      层状云降水效率通常较低，但却具有较高的云水资源开发潜力，是人工增雨作业的重要对象。随着中国南方地区生态改善、水库增蓄、抗旱等社会需求的增加，针对这些地区降水云系的人工增雨研究显得愈发重要。使用三维中尺度冷云催化模式，对2018年10月21日湖北省一次层状云飞机人工增雨作业过程进行了数值模拟研究，并将模拟结果与卫星、降水和机载云物理观测数据进行了对比。模式合理地模拟出了云和降水的主要宏、微观特征，观测和模拟结果均显示作业云区具有较好的冷云催化条件，在此基础上，按照实际作业中的飞机播撒轨迹，完整地模拟了此次催化作业过程。对数值模拟结果的分析表明：凝结冻结核化和凝华核化是碘化银催化剂的主要核化方式；90%以上碘化银粒子的局地活化比为0.01%—2%，平均活化比为0.07%—0.27%；云系降水是由冷云降水和暖云降水两种机制共同作用的结果，催化作业使两种降水机制均有增强，增雨效果明显；催化后4 h，整个评估区内的累计净增雨量为2.12×10⁸ kg，局地增雨率为-51.1%—306.7%，区域平均增雨率为8.1%；催化作业也使部分地区出现减雨，主要是由于催化过程中的潜热释放引起过冷层动力场扰动，一部分云区的上升气流减弱，从而导致降水粒子的成长减弱，地面出现减雨；在过冷云区，碘化银核化使冰晶浓度升高，导致冰晶-雪、雪-霰的转化过程增强，雪、霰粒子总量增加，更多的雪、霰粒子从冷区落入暖区，在暖区上层产生更多的大雨滴，从而使暖区的云雨粒子碰并过程增强，最终地面降水增加，这是此次催化作业导致增雨的主要微物理链条。

英文摘要:

      The precipitation efficiency of stratiform clouds is usually low, and thus stratiform clouds have a high potential for the development and utilization of cloud water resources. They are important targets for artificial precipitation enhancement. With the increasing demands for ecological improvement, reservoir storage, drought resistance, and other social needs in southern China, it is increasingly necessary to study the technology and mechanism of cloud seeding in stratiform cloud precipitation system over this region. In this paper, a three-dimensional mesoscale cold cloud seeding model was used to simulate the stratiform cloud system rainfall process and silver iodide (AgI) seeding operation by aircraft for rainfall enhancement in Hubei province, China on 21 October 2018. The main macro and micro characteristics of clouds and rainfall were reasonably simulated. Both observational data and simulation results show favorable cloud condition for AgI seeding in the aircraft operation area. On this basis, the entire aircraft seeding process along the real flight trajectory and seeding information were simulated. The numerical simulation results show that condensation-freezing nucleation and deposition nucleation are the main nucleation modes of AgI during the seeding operation. The local activation ratio of ice nuclei ranged from 0.01% to 2% for more than 90% of AgI, and the average value of AgI activation ratio was between 0.07% and 0.27%. Rainfall was the result of joint effects of cold cloud precipitation mechanism and warm cloud precipitation mechanism, and seeding operation enhanced the effects of the two precipitation mechanisms and achieved obvious rainfall enhancement effect. Four hours after the start of the seeding operation, the accumulated rainfall in the entire evaluation area increased by 2.12×10⁸ kg, which was equivalent to 8.1% of regional total rainfall; on local scale, the rainfall enhancement by seeding varied between −51.1% and 306.7%. Due to the dynamic disturbances caused by seeding in the supercooled cloud region, updrafts were weakened in some areas. As a result, the growth of precipitation particles was weakened and rainfall reduced in these areas. Seeding AgI in supercooled cloud region could lead to high concentration of the ice crystal particles, and the conversion processes from ice crystals to snow and from snow to graupels were enhanced. Following the increases in snow and graupel particles, more snow and graupel particles fell into the warm region of the clouds, and more large raindrops were generated in the upper layer of the warm region, which enhanced the collision-coalescence process between raindrops and cloud droplets in the warm region, and eventually led to rainfall increases. The above processes formed a main microphysical chain of rainfall enhancement by AgI seeding.