Rainfall: when supercooled water in the form of droplets that are still in liquid state in the form of ice crystals as the temperature is usually below 0 centigrade. The droplets are too heavy to remain dangling in the air and fall on the earth melting on their way.
Cloud seeding: the process to simulate precipitation and form rain by using dry ice, or silver iodide aerosols, into the upper part of clouds is known as cloud seedling. As known most of the rainfall starts over the ice crystals of the super cooled cloud droplets, by using the silver iodide particles the growth of new ice particles is encouraged. Be it summer or winter clouds are not potent enough at producing precipitation. Few parts of the storm are not 100% efficient to turn clouds into precipitation.
There are mainly 3 cloud seeding methods
Static cloud seeding: involves scattering a chemical like silver iodide into clouds. The silver iodide offers a crystal around which moisture can condense. The moisture is already available in the clouds, but silver iodide basically makes rain clouds more effective at giving out their water.
Dynamic cloud seeding: target is to boost vertical air currents, which boosts more water to pass through the clouds, translating into more rain. More ice crystals are used in dynamic cloud seeding than in the static method, up to 100 times more. This process is complex than static clouding seeding because it depends on a sequence of events functioning correctly in separate stages. An unanticipated outcome in one stage could collapse the entire process, making the technique less reliable than static cloud seeding.
Hygroscopic cloud seeding: scatters salts through bursts or explosives in the lower portions of clouds. As water joins with them the salts grow. It is said that hygroscopic cloud seeding holds much potential, but additional research is required.
Chemicals that are commonly used for cloud comprise silver iodide, dry ice, liquid propane, have been used. The usage of hygroscopic materials such as table salt is becoming more prevalent after positive result from research.
Silver iodide can cause momentary incapacitation or possible residual injury to humans and mammals with forceful or continued but not chronic exposure. However, several detailed ecological studies indicated negligible environmental and health impacts. The toxicity of silver iodide was shown to be of low order. These findings likely result from the minuscule amounts of silver generated by cloud seeding, which are 100 times below the industry emissions, or individual exposure from tooth fillings. Accumulation in vegetation, soil and surface runoff has not been above natural background. Those countries that employ cloud seeding to maintain a level of precipitation which is high enough to support their country must consider the countries downstream regarding the rainfall which they were to receive if the clouds not were seeded.