Suitability of cloud conditions for artificial rainfall enhancement by aircraft

based on data obtained from many events of aircraft rainfall enhancement operations，the suitable weather systems and patterns for artificially seeding supercooled clouds，the macro-physical characteristic of clouds for seeding，the micro-physical characteristics and the suitable conditions of precipitating stratiform clouds of cold front returning weather systern for seeding are analyzed．Results suggest that rainfall enhancement could be easily achieved when clouds are under conditions of less than 2km of cloud base height．more than 2km of cloud thickness，more than 1．5km of the supercooled layer,4．O～5．5km of seeding height，temperature ranging from -6～-13℃ and in developing stage of the weather system. There are two main cloud layers vertically in the spring cloud front weather system，i．e．． As layer above the frontal surface and Sc layer below the frontal surface．when ralnfall is about to occur，there is Fc near the ground．Parpticle Measuring Systems(PMS)data indicate that there are two layers with high liquid water content，corresponding to the middle parts of As and Sc respectively．The analysis suggests that this type of cold front weather system could be seeded for artifieial rainfall enhancement in spring and in wummer in Hebei Province．