Study of Physical Response of Cloud for Typical Stratiform Cloud Seeding

A seeding and contrast detection project was designed-based on the seeding area and leeward region which may collect response value by calculating the sounding and real-time radar data of a stratiform cloud system in Yan′an in spring of 2003.The PMS data of seeding and detection experimentation according to this project indicates that the concentration of big crystal increases in evidence while the number of cloud droplet decreases after 30 min seeding;the ice crystal are mostly hexagonal plates before seeding and the tapioca snow after that;the concentration of snow crystals (especially the big crystals) are increasing and the bigger snowballs are formed by several little snowballs after seeding.The radar echo shows that the cloud body is bigger evidently and the radar echo intensity increases 5~10 dBz after seeding;the precipitation of seeding area increases after 1 h seeding.It indicates that the seeded artificial ice crystals make ice crystal coagulation more helpful for super cold cloud transforming to rainfall than water droplet coagulation.Ice crystal effect and snow crystal aggregation are the main processes of this stratiform cloud rainfall system,in addition to the increased cloud rising speed from latent heat of super cold water solidification,these factors cause the development of cloud and rainfall in seeding area.