Study on Physical Structure of Hebei Stratiform Clouds in Autumn and Its Seedability Condition

By using the data of the aircraft observations( or operations) in Weather M odification Office of Hebei Province from 2006 to 2010,statistical characteristics of 29 clouds from 9 flights collected mainly in stratiform clouds over Hebei area in autumn are presented,including number concentration of aerosol,CCN,small cloud particles,large cloud particles,precipitating particles and cloud particle effective diameter. It has been found that midde-low level or high midde-low level stratiform clouds are the appropriate clouds for precipitation modification over Hebei area,w hereby clouds obtain enhancement due to supercooled layer catalytic,contributing to the positive feedback of airflow. The case studies demonstrate that the supercooled layer indicators appropriate for seeding are operation altitude of 4582 m and liquid w ater content of no less than 0. 1 g ·m- 3,associated with temperature of- 8. 0℃ and small cloud particle concentration of 236. 5 cm- 3.