一次飞机冷云增雨作业效果检验

Effect evaluation of an operational precipitation enhancement in cold clouds by aircraft

最近60多年,全球范围内广泛开展了人工增雨作业,但人工增雨效果检验一直是个难题。传统上,利用雨量计和目标/对比区统计数据评估人工增雨效果,结果大多不确定。对一次人工增雨作业而言,从科学上给出令人信服的效果检验更是没有好的解决方案。2017年3月19日,陕西省实施业务飞机冷云增雨作业播撒含有750 g碘化银(AgI)的催化剂,播撒线长125 km。作业后卫星、雷达观测到一条与播云线对应的清晰的云迹线,地面雨滴谱仪观测到相应的雨强、雨滴数浓度、雨滴直径增大,表明播云使云体产生了增雨响应。针对这次增雨过程,从连片雷达回波中分离增雨作用造成的回波增强带(增雨影响回波)和确定了自然降水回波强度,建立增雨影响回波强度(Z)与地面雨强(I)的拟合关系(Z-I关系),定量研究人工增雨的时、空演变。结果表明:(1)增雨影响时间约4 h,增雨影响回波区域(增雨影响区)面积为5448 km^(2)。该区累计降雨总量和增雨总量分别为1.518×10^(6) m^(3)和8.04×10^(5) m^(3),增雨影响区内增雨率达53%。(2)总降雨量、增雨量、自然降雨量随时间先增后减,总降雨量与增雨量的峰值同步,两者峰值都早于自然降雨峰值;催化后146 min(04时47分,世界时,下同),每6 min增雨量达到最大,为4.9×10^(4) m^(3);催化后174 min(05时15分),增雨雷达回波面积达到最大(1711 km^(2)),面积峰值滞后增雨量峰值出现。(3)增雨影响区位于播撒线下游,呈条带状;区域内总降雨量空间分布为中间大边缘小,与增雨量空间分布一致。(4)此次增雨作业改变了降雨时、空分布,促进降雨形成,增加了地面降雨量。

In the latest 60 years,artificial precipitation enhancement has been widely carried out around the world.However,the effect of artificial precipitation enhancement has not been evaluated comprehensively due to the lack of necessary information.Traditionally,statistic methods are used to evaluate the efficiency of artificial precipitation by comparing precipitation at the target area and the control area.Yet such methods have great uncertainties.Generally,there is no good solution to give convincing and scientific evaluation for an operational artificial precipitation enhancement.On 19 March 2017,an operational precipitation enhancement in supercooled stratiform clouds by aircraft was carried out in Shaanxi province.In this operation,750 g silver iodide(AgI)was seeded along a 125 km seeding line,which resulted in a clear cloud track corresponding to the cloud seeding line that could be observed by satellite and radar.The corresponding increases in rain intensity,raindrop number concentration and raindrop diameter were also simultaneously observed by raindrop spectrometers on the ground.The above observations show the linkage between cloud seeding and enhanced precipitation from the perspective of microphysical properties.Aiming to solve the problem of effect evaluation on rain enhancement,a new method is proposed based on comprehensive analyses of the observational data in this operation.In this method,the enhanced radar echoes caused by cloud seeding are separated from the continuous radar echoes to determine the background echoes(natural precipitation echoes).A fitting relationship is established between rain enhancement echoes and rain intensity(Z-I)on the ground to quantitatively study the effect of artificial rain enhancement.The results show that:(1)The effective time of precipitation enhancement is about 4 h,and the area influenced is 5448 km^(2) for this operation.The total precipitation and total enhanced precipitation are 1.518×10^(6) m^(3) and 8.04×10^(5) m^(3) respectively,and the rate of precipitation enhancement is 53%in the area influenced.(2)Total precipitation,enhanced precipitation and natural precipitation increased first and then decreased with time,the peak value of total precipitation occurred simultaneously with that of the enhanced precipitation and earlier than that of natural precipitation.After cloud seeding,the enhanced precipitation reached its maximum of 4.9×10^(4) m^(3) at 146 min(04:47 UTC),and the area of radar echo reached its maximum of 1711 km^(2) at 174 min(05:15 UTC).The peak of the former occurred later than that of the latter.(3)The influenced area of precipitation enhancement is located in the down reaches of the moving seeding line in a form of strip while total precipitation in this area is larger at its center and smaller at its edge,which is consistent with the spatial distribution of enhanced precipitation.(4)This operation changes the temporal and spatial distribution of precipitation and promotes the formation of precipitation.