عنوان مقاله [English]
Despite many successes in the field of freezing nucleation during the last two decades, there are still uncertainties and questions that have been of special interest to cloud physicists. Due to the wide variety of nucleation processes, most of the concepts expressed to describe the subject, could not bring forward comprehensive explanations. Using cold plate and fishing line apparatus, the immersion freezing nucleation rates of some natural materials such as, distilled water, smog, clay and leaf would have been studied. The seeding efficiency of natural material solutions have been studied through spraying them over the drops of distilled water suspended on the fishing line. The experimental results confirm the time-temperature dependence of freezing rate due to heterogeneous nucleation. They also show that a good cloud seeding agent can be easily produced from bacterial biogenetic nuclei as effective nucleation materials. By deduction the effect of contact freezing, the biogenetic nuclei are found to have maximum activity at -5°C and their seeding efficiency is about 80% at -9°C. These results are more acceptable than those of mineral substances such as Silver Iodide. The performance of these experiments in a clean weather or the use of the bacteria incubation method, leads to more accurate and reliable results. Performing such low-cost experiments, not only could bring out a better understanding of the freezing nucleation process, but it is also possible to decrease the expences of cloud seeding projects as well as the dangers of airplane accidents inside the clouds.