Ī study conducted by the National Academy of Sciences failed to find statistically significant support for the effectiveness of cloud seeding. Whether cloud seeding is effective in producing a statistically significant increase in precipitation is still a matter of academic debate, with contrasting results depending on the study in question, and contrasting opinion among experts. įurther information: Laser-assisted water condensation Effectiveness The experimenters posited that the pulses would encourage atmospheric sulfur dioxide and nitrogen dioxide to form particles that would then act as seeds. Infrared laser pulses Īn electronic mechanism was tested in 2010, when infrared laser pulses were directed to the air above Berlin by researchers from the University of Geneva. For instance, in Al Ain it rained 6.9 millimetres on 20–21 July. This method produced a significant rainstorm in July 2021. Since 2021, the United Arab Emirates has been using a new technology: drones equipped with a payload of electric-charge emission instruments and customised sensors fly at low altitudes and deliver an electric charge to air molecules.
When released by devices on the ground, the fine particles are carried downwind and upward by air currents after release. For release by aircraft, silver iodide flares are ignited and dispersed as an aircraft flies through the inflow of a cloud. Ĭloud seeding chemicals may be dispersed by aircraft or by dispersion devices located on the ground (generators or canisters fired from anti-aircraft guns or rockets). This strategy of "dynamic" seeding assumes that the additional latent heat adds buoyancy, strengthens updrafts, ensures more low-level convergence, and ultimately causes rapid growth of properly selected clouds. Seeding of warm-season or tropical cumulonimbus (convective) clouds seeks to exploit the latent heat released by freezing. This process is known as "static" seeding. If sufficient growth takes place, the particles become heavy enough to fall as precipitation from clouds that otherwise would produce no precipitation. The formation of ice particles in supercooled clouds allows those particles to grow at the expense of liquid droplets. In mid-altitude clouds, the usual seeding strategy has been based on the fact that the equilibrium vapor pressure is lower over ice than over water. Introduction of a substance such as silver iodide, which has a crystalline structure similar to that of ice, will induce freezing nucleation. When cloud seeding, increased snowfall takes place when temperatures within the clouds are between −20 and −7 ☌. After promising research, the use of hygroscopic materials, such as table salt, is becoming more popular. This can produce ice crystals at higher temperatures than silver iodide. Liquid propane, which expands into a gas, has also been used.
The most common chemicals used for cloud seeding include silver iodide, potassium iodide and dry ice (solid carbon dioxide).
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Its effectiveness is debated some studies have suggested that it is "difficult to show clearly that cloud seeding has a very large effect." The usual objective is to increase precipitation (rain or snow), either for its own sake or to prevent precipitation from occurring in days afterward. Ĭloud seeding is a type of weather modification that aims to change the amount or type of precipitation that falls from clouds by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud. The process shown in the upper-right is what is happening in the cloud and the process of condensation upon the introduced material. ( January 2021)Ĭloud seeding can be done by ground generators, planes, or rockets This image explaining cloud seeding shows a substance - either silver iodide or dry ice - being dumped onto the cloud, which then becomes a rain shower. Please consider expanding the lead to provide an accessible overview of all important aspects of the article. This article's lead section may be too short to adequately summarize the key points.
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