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What is Cloud Seeding?

Description: Exploring Cloud Seeding: How Artificial Rainfall Is Achieved and Its Environmental Concerns. Discover the process, methods, and environmental challenges of cloud seeding, a technique used to induce artificial rainfall.

Cloud seeding or weather modification is an artificial way to induce moisture in the clouds so as to cause rainfall. 

Process of cloud seeding

•  Aircraft, mini-blasting rockets (explosive rockets), and Balloons may be used in cloud seeding ‘ 

•  Through the cloud seeding process with the help of Aircraft silver iodide (dry-free) is sprayed into the cloud. 

•  Silver iodide attracts the water drops that already exist in the clouds. When they come contest in the dry ice they convert into the drops. And these drops fall in the form of rain on the earth. 

•  Commonly the range of or distance of clouds 1-2 km from the earth, this technique is implemented (these clouds are also called Nimbus clouds). 

•  The color of the clouds is brownish.

•  After that process the rain may fall after or within 15-20 minutes of the cloud seeding.

Chemicals used for cloud seeding

•  Silver Iodide

•  Potassium Iodide

•  Carbon Dioxide

•  Propane

•  Calcium Carbide

•  Ammonium Nitrate

•  Sodium Chloride

•  Urea Compound

Methods of cloud seeding

There are three cloud seeding methods: static, dynamic and hygroscopic.

•  Static cloud seeding involves spreading a chemical like silver iodide into clouds. The silver iodide provides a crystal around which moisture can condense. The moisture is already present in the clouds, but silver iodide essentially makes rain clouds more effective at dispensing their water.

•  Dynamic cloud seeding aims to boost vertical air currents, which encourages more water to pass through the clouds, translating into more rain. Up to 100 times more ice crystals are used in dynamic cloud seeding than in the static method. The process is considered more complex than static clouding seeding because it depends on a sequence of events working properly. 

(1) the nucleated ice crystals glaciate a large volume of the cloud releasing the latent heat of freezing and vapor deposition, (2) this warms the cloud yielding additional buoyancy in the seeded updrafts, (3)the updrafts with enhanced buoyancy accelerate causing the cloud towers to ascend deeper into the troposphere, (4) pressure falls beneath the seeded cloud towers and convergence of unstable air in the cloud will as a result develop, (5) downdrafts are enhanced, (6) new towers will therefore form, (7) the cloud will widen, (8) the likelihood that the new cloud will merge with neighboring clouds will therefore increase, and (9) increased moist air is processed by the cloud to form rain.

•  Hygroscopic cloud seeding disperses salts through flares or explosives in the lower portions of clouds. The salts grow in size as water joins with them. 

Conditions needed for cloud seeding 

•  Cloud seeding only occurs when the cloud is in a developing stage. 

•  It cannot be done in dry weather conditions.

•  The silver iodide seeding is used when the cloud top temperature of the cumulus cloud formation is 23o F 26 to 26o F (-3o C to –5o C) or colder or when the cloud growth indicates that it will shortly reach that temperature level soon in the atmosphere. The main objective of cold cloud seeding is to initiate the dynamic latent heat release which will stimulate the growth of the cloud.

•  In the warm cloud seeding hygroscopic materials like common salt, calcium chloride or a mixture of Ammonium Nitrate and Urea that absorb water vapor from the surrounding air are used. The hygroscopic particles will gradually grow in size by condensation and then by coalescence with cloud droplets that grow into heavy drops that produce rainfall.

Issues in Cloud seeding 

• Bioaccumulation: Silver iodide chemical is most commonly used to seed a cloud and is known to be toxic for aquatic life because of bioaccumulation. o Bioaccumulation is a process of accumulation of chemicals in an organism that takes place if the rate of intake exceeds the rate of excretion. 

• Increasing Carbon footprint: Cloud seeding through dry ice (Carbon dioxide) is the source of Greenhouse Gases and affects climate change. 

• Disturbing the Hydrological cycles: Cloud seeding simply redistributes rain in drought-affected areas which can ultimately affect the Hydrological cycles.

Here is a link to an article on Nipah virus