Atmosphere And Weather

How does Cloud Seeding Work to Increase Rainfall or Weather Modification or Cloud Seeding



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For many decades, scientists have experimented with producing artificial rain or snowstorms to counteract droughts or extreme temperatures experienced in different parts of the world. It is also known that Chinese officials used weather modification to stave off potential rainstorms or over-heating during the 2008 Beijing Olympics and that they were able to keep the sky clear over Beijing throughout the event. Cloud seeding is one such weather modification method used by many different countries including the United States and is a topic of interest in many global forums dealing with environmental issues.

The principle behind cloud seeding

The basic principle behind cloud seeding is condensing the available precipitation within the clouds to form raindrops using an artificial chemical or a gas, which provides the cloud with an efficient nucleus to attract precipitation. The commonest chemical substance to be used for cloud seeding is silver iodide, although dry ice has also been used in some instances. The reason to use silver iodide instead of other substances to condense precipitation is that silver iodides microstructure or the lattice structure mimics the structure of dry ice, which is an excellent attractor of precipitation, in many different ways. However, in order to produce adequate condensed precipitation, silver iodide requires already formed droplets or particles whereas the other forms can harness spontaneous nucleation through cooling the surrounding vapor.

Modes of delivering the chemical for cloud seeding

In order to deliver these chemicals to a cloud location, scientists have made use of aircrafts which can disperse the chemical as it flies through the cloud. On the other hand, canisters filled with the substance can be fired from the ground using anti-aircraft guns or other type of firing device and upon reaching the intended height; the canisters explode and disperse the chemical constituents.

Types of cloud seeding

The cloud seeding described earlier refers mainly to a method called the ‘static could seeding’. In contrast, a more complex method known as ‘dynamic cloud seeding’ make use of far more ice crystals than ‘static cloud seeding’ to generate a vertical air current which encourages more water to pass through the cloud and therefore more likelihood towards condensing. However, scientists rely less on the outcome of a ‘dynamic cloud seeding’ because it involves multiple stages and failure at any level can lead to a failure of the entire cloud seeding process. Thirdly, a method known as ‘hygroscopic cloud seeding’ make use of salts dispersed at a lower portion of the clouds to generate water drops although the method require more scientific research in order to produce effective results.

Controversies regarding weather modification

Although cloud seeding seems to be a promising weather modification method, it does have its own critics. For instance, the United States National Academy of Sciences declared in 2003 that, ‘after 30 years of research, there is no convincing evidence to suggest that weather modification actually works’. However, illustrating the unclear and controversial nature of weather modification science including cloud seeding, the American Meteorological Society declares that, ‘some studies in cloud seeding have shown a 10% increase in the rain volume’.

Thus, cloud seeding is a method which will have to cross many obstacles and ethical barriers before it becomes a useful tool for sustainability of the human race without harming the balance of the Mother Nature.

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More about this author: Dr Pandula Siribaddana

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ARTICLE SOURCES AND CITATIONS
  • InfoBoxCallToAction ActionArrowhttp://science.howstuffworks.com/nature/climate-weather/meteorologists/cloud-seeding.htm
  • InfoBoxCallToAction ActionArrowhttp://www.swhydro.arizona.edu/archive/V6_N2/feature1.pdf
  • InfoBoxCallToAction ActionArrowhttp://science.howstuffworks.com/nature/climate-weather/meteorologists/cloud-seeding2.htm