层状云催化宏微观物理响应的数值模拟研究

层状云系是进行人工增雨开发利用空中云水资源的重要对象，增雨作业需要有科学可行的技术指标来指导实际作业的科学实施，而合理准确评估人工增雨作业的效果也是需要解决的重要课题，通过数值模式合理地仿真模拟实际催化作业的过程，进而研究增雨作业后云和降水的一系列宏微观特征的变化及其机理，是建立和改进催化作业技术的必要途径，也是评估实际人工增雨作业效果的有效手段。本文使用三维中尺度冷云催化模式对2014年4月15日河北省一次层状云降水的飞机催化作业过程进行了仿真模拟，力图对实际作业过程进行合理再现，通过对模拟结果的分析，研究飞机播撒的AgI（Silver iodide）催化剂在空中的扩散传输特征，分析催化对云和降水宏微观特性的影响，并对此次飞机催化作业的增雨效果进行评估。研究结果表明，播撒的AgI催化剂烟羽扩展的水平尺度可达数十公里以上，垂直方向上，大部分AgI粒子则主要集中在作业层上下约1 km的厚度范围内，AgI粒子的向上输送明显强于向下的输送；催化后云中的冰晶和雪粒子明显增加，导致催化模拟前期的霰增长受到抑制，之后随着霰碰并雪过程及零度层附近冰相粒子淞附过程的增强，云中霰的总量逐渐增加；催化作业后，催化云的雷达回波强度有明显增强，且随时间变化表现出不同的结构特征；催化导致地面降水出现先减少后增加的时间变化特征，催化后3小时，作业影响区向作业区下游扩展100 km以上，总体呈现减雨—增雨的区域分布特征；数值模拟评估表明，整个评估区内的净增雨量达到3.6×107 kg，平均增雨率为1.1%，暖层霰粒浓度和尺度的增加是降水增加的主要原因。由于作业目标云系的催化条件一般，而播撒的AgI剂量偏大，造成增雨作业效果偏低。

Numerical Simulation of the Macro and Micro Physical Responses of Stratiform Cloud Seeding

Stratiform cloud systems are important for the exploitation and utilization of cloud water resources. Precipitation enhancement requires scientific and feasible operational technical indicators to guide the implementation of actual operations, and a reasonable and accurate assessment of operation effects is an important issue that needs to be solved. One of the necessary ways to establishing and improving operation technologies is to simulate the seeding operation process reasonably through a numerical model and study the changes and mechanisms of a series of macro and micro characteristics of cloud and precipitation after seeding operations. Evaluating the effect of realistic precipitation enhancement is also an effective method through a seeding model simulation. An aircraft seeding operation during the stratiform cloud precipitation in Hebei province on April 15, 2014 was simulated in accordance with a real operation process by a 3D mesoscale cold cloud seeding model. The actual operation process was reasonably simulated by the numerical model. The diffusion and transmission characteristics of AgI particles seeded by aircraft in the atmosphere were studied, the seeding influence on the macro and micro characteristics of clouds and precipitation was analyzed, and the precipitation enhancement effect of the aircraft seeding operation was evaluated. Results show that the horizontal scale of AgI plume can extend to more than tens of kilometers, and most AgI particles in the vertical direction are concentrated within the range of approximately 1 km above and below the seeding layer. Moreover, the upward transport of AgI particles is significantly stronger than the downward transport. The outstanding increase in ice crystals and snow particles in clouds after seeding leads to the inhibition of graupel growth in the early simulation stage. However, the enhancement of the graupel collection snow process and ice phase particle riming processes near the zero layer gradually increases the total mass of graupel after some time. After the aircraft seeding operation, radar reflectivity is enhanced; in addition, it shows different structural characteristics with time. Precipitation decreases first and then increases with time due to seeding. Three hours after seeding, the operation influence area extends to more than 100 km to the downstream of the operation area, showing the distribution characteristics of rainfall-reducing area first and then rainfall-increasing area in general. The model evaluation indicates that the net rainfall increases by 3.6×107 kg in the entire evaluation area, with an average rainfall-increasing rate of 1.1%; furthermore, the increase in the concentration and size of graupel particles in the warm layer is the main reason for rainfall increase. Given the weak seeding operation conditions in the target cloud area, the AgI seeding amount of this operation is relatively high, resulting in a low effect of precipitation enhancement.