During the last twenty years, heterogeneous freezing nucleation has been one of the important fields of study in meteorology, and, it has been of special interest to cloud physicists. However, despite much success in this field there remain numerous ambiguities in the ice nucleation process.
Using both, cold plate and fishing line apparatus, the drop freezing rate due to heterogeneous nucleation has been studied at constant temperature and constant cooling on rain samples over Gilan (near the north coast of Iran) during the autumn and winter, 2000-200 1.
The immersion freezing nuclei concentrations obtained in cumuliform (14.31-20.44 m3) and stratiform (11.9-13.8 m3) clouds are in good agreement with the results of previous researchers as Vali (1994), Cooper and Lawson (1984), Rogers and Yau (1996). These are, however, much less than the amounts reported by various cloud seeding projects faced with over seeding problem. Therefore, Gilan area clouds have very good seeding potential. These results can provide valuable information about recognizing cloud systems in the experimental area, and let physicists predict the success of their cloud seeding program projects.
Before carrying out any artificial cloud seeding project, it is necessary to do some laboratory experimental work to prevent unnecessary expense. These low-cost experiments, not only, decrease the economic coefficient of efficient cloud seeding projects, but also the danger of airplane accident inside the clouds