中国气象科学研究院 中国气象局人工影响天气中心 北京,100081
Stratiform cloud system is important object 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 reasonable and accurate assessment of operational effects is an important issue that need to be solved. It is a necessary way to establish and improve the operation technology to simulate the actual seeding operation process reasonably by numerical model, and then study changes and mechanism of a series of macro and micro characteristics of cloud and precipitation after seeding operation. It is also an effective method to evaluate the effect of practical precipitation enhancement operation. An aircraft seeding operation during the stratiform cloud precipitation in Hebei province on April 15, 2014 was emulationally simulated by a 3D mesoscale cold cloud seeding model. The actual operation process was reasonably simulated by the numerical model. The diffusion and transmission characteristics in atmosphere of AgI particles seeded by aircraft was studied, and seeding influence on the macro and micro characteristics of cloud and precipitation was analyzed, and precipitation enhancement effect of the aircraft seeding operation was evaluated. The results show that the horizontal scale of AgI plume can extend more than tens of kilometer, and most of AgI particles in the vertical direction are concentrated within the range of about 1km above and below the seeding layer. The upward transport of AgI particles is significantly stronger than the downward transport. The outstanding increase of ice crystals and snow particles in the cloud after seeding operation lead to the inhibition of graupel growth in the early simulation stage. However, the enhancement of graupel collection snow process and ice phase particles riming processes near zero layer gradually increase total mass of graupel after some time. After the aircraft seeding operation, the radar reflectivity has obvious enhancement and show different structure characteristics with time. The precipitation decreases first and then increase with time as a result of seeding. Three hours after seeding, the operation influence area extended more than 100km to the downstream of the operation area, and showing the distribution characteristics of rainfall-reducing area first and then rainfall-increasing area in general. The model evaluation indicates that the net rainfall increased by 3.6×107kg in the entire evaluation area, with an average rainfall-increasing rate of 1.1%, and increase of graupel particles concentration in warm layer is the main reason for rainfall increase. Due to the weak seeding operating conditions in the target cloud area, AgI seeding amount of this operation is relatively high, resulting in little effect of precipitation enhancement.