The Experiment of Ice Nucleus Generating Efficiency by Model 37 Silver Iodide Shell

Model 37 shell is one of the main carrier of silver iodide catalytic agent usedin rainfall enhancement and hail suppression operations. Nucleating effectiveness values of silver iodide filled in shell are important reference to measure the amount of silver iodide catalytic agent using in weather modification operation. Using a 1200 L isothermal cloud chamber and a 20 m³steel plate explosion chamber, the first uniform test of ice nucleus generating efficiency of model 37 silver iodide shells isimplemented by Weather Modification Center of CMA (WMC) from November to December of 2013, and samples chosen randomly from 2 manufacture factories is examined. Uucleation rates of two kinds of sample are detected at eight temperature between-3℃ to-20℃. Results show that fitting values of nucleating effectiveness of two kinds of samples are all in the range of 10⁹-10¹²/(g·AgI) with the temperature from-6 ℃ to-20℃, and the threshold temperature is-4℃. The nucleating effectiveness of sample 2 is higher than that of sample 1 obviously, and the maximum difference of fitting values between them is 8.4 times at-14℃. The comparison between this experiment and past results given by domestic different experiments is carried out. Results indicate the nucleation rates of sample 1 and sample 2 are higher than the past results at-14℃ above, and they are both 2 to 3 orders of magnitude more effective than the detection values of past experiments at-10℃. To seek cause for this significant difference, a detailed comparative analysis onexperiment condition is carried out. Some techniques applied to the 1200 L isothermal cloud chamber such as temperature controlling, fog making and ice crystals counting are improved, and impacts of those operations are reduced. Meanwhile, larger volume of cloud chamber results in less border effect, and longer time of holding fog in cloud chamber, so it simulates actual atmospheric condition better. Based on above discussions, the testing results of model 37 silver iodide shell nucleation rate are reliable. Furthermore, in view of the great deviation in different experiments, it is very necessary to uniformly test nucleation rate of seeding agent on the same experiment platform.