吸湿性播撒对暖性对流云减雨影响的数值模拟

Numerical Simulation of Hygroscopic Seeding Effects on Warm Convective Clouds and Rainfall Reduction

利用以色列特拉维夫大学二维面对称分档云模式(two-dimensional slab-symmetric detailed spectral bin microphysical model of Tel Aviv University),对2016年9月4日16:00(北京时)前后我国华东地区的一次暖性浅对流云降水过程进行模拟,模式模拟的强回波中心高度和最大回波强度范围与观测基本一致。并在此基础上进行了小于1μm的吸湿性核的播撒减雨试验,分别考虑了不同播撒时间、不同播撒高度以及不同播撒剂量的敏感性测试。结果表明:在云的发展阶段早期播撒能起到更好的减雨效果,播撒时间越早对大粒子生长过程的抑制作用越强,随着播撒时间向后推移,受抑制作用最显著的粒径段向小粒径端偏移;在云中心过饱和度大的区域下方进行播撒,减雨效果更加明显,当播撒剂量为350 cm^(-3)时,地面累积降水量减少率可达23. 3%;另外,随着播撒剂量的增加,减雨效果更加显著,甚至能达到消雨的效果。因此,在暖性浅对流云中合理地播撒小于1μm的吸湿性核能达到较好的减雨或消雨效果。

With the rapid development of social economy, the frequency of various large-scale and important events is also getting higher and higher. In order to host events more smoothly, the need of society for artificial precipitation suppression technologies during major events is also urgent. Hygroscopic seeding is an important way to suppress precipitation artificially. Although previous research on artificial precipitation suppression basically confirms that the hygroscopic nuclei of smaller than 1 μm can inhibit the convective cloud precipitation, how to use it more effectively to achieve the best effect is still a difficult problem in precipitation research. In order to provide some useful theoretical references for artificial precipitation suppression operations, a two-dimensional slab-symmetric detailed spectral bin microphysical model of Tel Aviv University in Israel is used to simulate the warm shallow convective cloud and precipitation in East China at about 1600 BT on 4 September 2016. The height of the strong radar reflectivity center and the range of high radar reflectivity are basically consistent with observations. The cloud seeding experiments with hygroscopic nuclei smaller than 1 μm are conducted in order to examine sensitivities of seeding effects to seeding time, seeding height and seeding amounts of particles, respectively. Results show that the early seeding in the cloud development stage can lead to more significant effect on rainfall suppression. The earlier the seeding time is, the stronger the inhibition of the growth of large particles. As the seeding time goes backwards, the particle size segment with the most significant inhibition shifts to smaller particle size;the effect of rainfall suppression is more obvious when seeding is carried out just below the area with large supersaturation in the center of cloud. Since a large number of hygroscopic nuclei seeded here enter the supersaturation zone, they are activated to be small cloud droplets, and the cloud water conversion and collision process are suppressed. The reduction rate of ground accumulated precipitation reaches 23. 3%when the seeding concentration is 350 cm-3. In addition, with the increase of seeding amounts of hygroscopic nuclei, the precipitation suppression effect is more significant, and the rain is even eliminated.Therefore, seeding hygroscopic nuclei smaller than 1 μm properly in warm shallow convective clouds can achieve expected results of reducing or eliminating rain.