Cloud seeding is the process when chemicals like silver iodide, calcium chloride, salts or dry ice are shot into the topmost layers of the clouds.
This is in order to cause rain after stimulating the precipitation process. This process is also known as weather modification. The aviation industry has used it to enhance visibility in busy airports by eradicating fog. Nevertheless, it is also used to minimize hailstorms, increase the precipitation of the clouds. It is used to reduce the intensity of hurricanes or to achieve clear skies during large sporting events. A good example is the Beijing Olympics of 2008 in China.
How does it work?
The underlying mechanism of cloud seeding is deduced from the natural process of rainfall formation. Rainfall occurs when supercooled water comes in contact with particles of dust ice crystals in the clouds. These ice crystals form tiny nuclei made up of either be solid or liquid particles that are found in the atmosphere. Water droplets usually attach to these nuclei, increasing their size. Once they are large enough these droplets fall like rain or like snow in colder regions.
Cloud seeding mimics this process. It increases the quantity of the nuclei available in the atmosphere by the addition of tiny particles. This is done by sowing elements in the cloud. These added nuclei, increase the precipitation of the cloud. Which causes rainfall in places and times that it would not normally occur.
Types of cloud seeding
- Static cloud seeding :
This method involves sowing chemicals in the cloud. Chemicals like silver iodide are spread in the cloud in such a way that it provides the crystals that moisture can condense on. These chemicals take advantage of the moisture content of the cloud, enabling the rain clouds to effectively disperse water droplets.
- Hygroscopic cloud seeding
This method involves the dispersion of hygroscopic salts using explosives or flares in the lower layers of the clouds. The hygroscopic salts like calcium chloride, silver iodide sown grow in size as it attracts water droplets to attach to them and later becomes raindrops. This is also known as the warm rain process and is often used in tropical areas.
- Dynamic cloud seeding
In this method, rain is formed by increasing vertical air currents. This increases the moisture content of the clouds as more water is forced through the clouds. This method utilizes ice crystals 100 times more than the static method of cloud seeding. The effectiveness of this rain formation method depends on a series of factors which must be in place. In fact, a little anomaly at any stage could nullify the whole process. This explains why it is considered a more complex and less reliable than other methods of cloud seeding.
Where has it been successful?
Cloud seeding has been considered to be effective in providing rainfall in different areas. Success has been recorded in trials in the United States, Spain, France, and Australia. This technique is noted to be behind about 52 storms in the deserts of Abu Dhabi.
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