2014年4月15日河北省中南部出现一次回流西风槽天气过程，河北省人工影响天气办公室对该天气过程作了飞机云物理探测和增雨作业，并专设飞行航线以研究作业前后云的宏观、微观物理响应。利用机载PMS观测资料，结合雷达、卫星观测资料分析，发现该次降水过程云系特点是上层"槽前云"较弱，下层"回流云"较强，无高云；作业探测过程中云中下沉的降水粒子在"回流云"中增长，该层出现大量直径在3 mm以上的降水粒子；作业层内小云粒子浓度普遍在20 cm-3以上，最大值为300 cm-3，大云粒子浓度低于0.02 cm-3。作业后宏微观物理响应包括：作业区FY-2E卫星云图亮温在1 h后由-25℃降到-30℃左右，中云发展，其云顶抬高；雷达反射率因子催化作业后升高，最强达45 dBZ，35 dBZ以上的雷达回波区面积增加；从雷达剖面图上看，强雷达回波区下沉了500~1000 m。机载PMS观测资料显示，作业后云中小云粒子、大云粒子浓度都有增加，降水粒子浓度经历了先降后升的过程，持续时间约25 min。粒子谱呈双峰分布，第二峰在10.5 μm；粒子浓度在直径在10.5~150 μm区间内呈指数递减，直径在150~1000 μm区间内粒子浓度变化不大而粒子直径迅速增长，大于1000 μm粒子浓度急降与粒子沉降有关；作业后有效粒子直径向大值方向偏移，平均直径、平方根直径和立方根直径分布频谱变宽，粒子分布更离散。作业后影响区地面雨量增加，影响时间在作业后3 h之内。
A synoptic reflux process of westerly trough occurred over the central and southern part of Hebei Province on 15 April 2014.The airplane detection on cloud physics combined with the artificial seeding operation was conducted by the Hebei Province Weather Modification Office, besides, a special flight route was designed to investigate the variation of the micro and macro physical parameters before and after the operation in this paper.This precipitation cloud system characteristics were analyzed based on the airborne Particle Measurement System (PMS) observation dataset, the radar and the satellite data.It is found that precipitation in the upper layer of "pre-trough cloud" was weaker than that in the lower reflux cloud, with no high cloud present.The descending precipitation particles growed in the "reflux cloud" during the operation observation, with large amounts of precipitation particles smaller than 3 mm in diameter existing in this layer.Small cloud particle number concentration normally was higher than 20 cm-3, with a maximum of 300 cm-3 in the operation layer.Large cloud particles number concentration lied below 0.02 cm-3.The macro and micro physical responses of cloud after the operation are as follows:The FY-2 satellite cloud image brightness temperature reduced from -25℃ to about -30℃, and the middle clouds developed with increased cloud top; Radar echo intensity increased after the seeding operation with a maximum intensity of 45 dBZ.The radar echo area larger than 35 dBZ in cloud was also increased; According to the radar sectional profile, the strong radar echo area dropped to 500~1000 m; Small cloud particles and large cloud particles number concentration were both increased, with precipitation number concentration increased first and then reduced, and the process lasted about 25 minutes based on the PMS observation dataset; The precipitation particle size distribution presented a bimodal distribution, with the second peak located at 10.5 μm.The number concentration of particles with diameters between 10.5~150 μm decreased exponentially.However, there was no significant change on the number concentration of particles with diameters between 150 to 1000 μm, although their diameters were found to be increased rapidly.The sharp decrease of the number concentration of particles with diameter larger than 1000 μm was associated with the particle deposition mechanism.The effective diameter of cloud moved to a higher value with a more disperse distribution of the average diameter, the square root diameter and cube root diameter, indicating a discrete particle distribution.The precipitation increased and kept three hours after the operation.
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