Wednesday, October 16, 2019

Artificial Precipitation (Rainfall)

Artificial Precipitation (Rainfall)

Artificial Precipitation also known as artificial rainfall and pluviculture, is the act of attempting to artificially induce or increase precipitation. Usually to stave off drought or the wider global warming.

It's a practice of artificially inducing or increasing precipitation through clouds by adding external agents. The foreign particles which are drenched over these clouds can be Dry Ice(solid carbon dioxide), Silver Iodide, Salt powder etc.

Can rain be created artificially?? The answer is Yes!!!
When the water drops in a cloud are too small or there are not enough ice crystals to create rainfall, we can use artificial ways to create ice crystals or help small water drops grow, and thereby facilitate the formation of precipitation. This human influenced weather phenomenon is called artificial rain.

Cloud Seeding

The first experiments with cloud seeding were conducted in 1946 by American chemist and meteorologist Vincent J. Schaefer, and since then seeding has been performed from aircraft, rockets, cannons, and ground generators. Vincent J. Schaefer was a self-taught chemist who invented cloud "seeding" and created the first artificially induced snow and rainfall.

All precipitation develops in clouds, and clouds are formed when water vapor in the atmosphere cools and condenses. As the water vapor condenses into it forms droplets and if the clouds develops within or moved into the part of the atmosphere that is below freezing then the droplets form ice crystals.

For the uninitiated, cloud seeding or weather modification is an artificial way to induce moisture in the clouds so as to cause a rainfall. In this process, either silver iodide or dry ice is dumped onto the clouds by using an aircraft or an artillery gun which leads to a rain shower.

In order for cloud seeding to work, there has to be rain clouds already present. By filling the cloud with silver iodide, they can increase the rainfall by 5 to 30 percent depending on where they clouds are located. ... The concern over silver iodide in our water and air supply is a real one.

The researchers report that in ideal conditions, seeding increased winter precipitation by 5 to 15 percent. A cloud seeding program in the region could cost $27 to $214 per acre-foot of water in a low cost scenario and $53 to $427 per acre-foot in a high-cost scenario.

The Principle of Artificial Precipitation

In the troposphere, the temperature of the atmosphere descends with altitude. Therefore the clouds in the troposphere are lower in temperature as they rise in altitude and vice versa. When the temperature of a cloud is above 0 °C, the cloud is called a warm cloud; when it is below 0 °C it is called a cold cloud. Inside a warm cloud, small water drops will become large ones through collision and coalescence, and will finally break the buoyancy of the cloud and fall out of its bottom to become rainfall to the ground. Likewise, inside a cold cloud, ice crystals can also grow to a size where they can break the buoyancy and fall out of the cloud's bottom, and when they pass through a temperature of 0 °C they will melt and become rain drops, also providing the ground with rain. When the water drops in a cloud are too small or there are not enough ice crystals to create rainfall, we can use artificial ways to create ice crystals or help small water drops grow, and thereby facilitate the formation of precipitation. This human influenced weather phenomenon is called artificial rain. 

There are many ways to make rain in a warm cloud, e.g. spraying water drops, hygroscopic powder or liquid (sodium chloride), etc, and letting the water drops grow though collision and coalescence to finally become rain. There are also many ways to make rain in a cold cloud, but the most common way is to use dry ice or silver iodide. This is mainly because the temperature of dry ice is -78 °C. Spreading dry ice in a cold cloud lacking ice crystals will rapidly reduce its temperature. Therefore we directly transform supercooled water into ice crystals, which will eventually become rain without the help of ice-crystal nuclei. Silver iodide, on the other hand, is a very effective ice-crystal nucleus. By adding it to a cloud, silver iodide acting as an ice-crystal nucleus can facilitate the solidification of water drops below -5 °C into ice crystals. Through the growing process the ice crystals under the coexistence of water drops, the rain will be formed.

Advantages of Artificial Precipitation

Disadvantages of Artificial Precipitation
Health problems and environmental impact ranges from storms like tornadoes, or suppression of the rainRain suppression would cause a very unfortunate impact on agriculture. This would result in several repercussions like lack of vegetation and crop harvest tends to get poorer.


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