Methods of Aircraft-based Precipitation Enhancement Operation for Convective-stratiform Mixed Clouds in Autumn in Hunan Province

Based on ground meteorological observations at Changsha of Hunan, and the aircraft artificial precipitation enhancement operation data in autumn of recent 10 years in Hunan, some statistical analysis results on the convective-stratiform mixed clouds systems are obtained, including the distribution of precipitation, structure characteristics and the seeding method of aircraft artificial precipitation enhancement operation.Physical characteristics of typical operation weather processes are analyzed by using Doppler radar data, the numerical model GRAPES_CAMS, and meso-scale meteorological data.Paired convective clouds and the echo tracking method based on TREC algorithm are used for effect evaluation.12 macro and micro parameters are picked out as indicators of artificial precipitation enhancement operation with convective-stratiform mixed clouds, including precipitation weather situation, the main cloud system, cloud-top height, cloud-top temperature, cloud thickness, seeding layer height, seeding layer temperature, seeding layer relative humidity, radar echo intensity, vertically integrated liquid, supercooled water content, rainfall situation and so on.The best seeding time, position and catalyst amount of the artificial precipitation enhancement operation using Yun-7 aircraft and AgI catalyst are discussed.For convective-stratiform mixed clouds including precipitus stratiform clouds and cumulus clouds, the most suitable area, seeding height and catalyst dosage of the operation are summarized.In supercooled -15 to -5℃ layer of altostratus cloud, seeding catalyst could make the artificial ice crystal concentration reach 30 L^-1; in supercooled -15 to -7℃ layer of cumulus cloud, static seeding catalyst makes the concentration 30 L^-1 while dynamic seeding catalyst makes it 100 L^-1.These operation methods achieves good results in the practice of artificial precipitation enhancement.Among more than 40 times aircraft precipitation enhancement operation practice in recent 8 years, cold cloud catalyst seeding in precipitus stratiform clouds in convective-stratiform mixed clouds system usually leads to light rain (1-10 mm); cold cloud catalyst seeding in cumulus clouds in convective-stratiform mixed clouds system usually lead to small to moderate rain (5-17 mm); another 4 operations of warm cloud catalyst seeding in relatively stable stratiform warm clouds maintaining more than 12 h only bring slight enhancement of precipitation (0.1 mm).In the future, airborne meteorological equipment should be developed for cloud physics detection, especially for the detection and study of cumulus.Based on improved performance indicators of cumulus seeding, the cloud physics concept model of cumulus cloud artificial precipitation in southern China can be gradually established.