By Vadim Sablo
|Cloud seeding is the amazing technology and process by which additional rain is artificially produced from a cloud. For those parts of the world where rain and water is less reliable and more valuable, this technology can potentially bring great benefit to environmental, agricultural, tourism and sustainable energy industries. |
Although Cloud seeding has huge potential benefits, this new technology is yet to reach its full potential. We investigate, along with two experts who have agreed to share their opinions with Ask The Experts.
TSR- Clouds contain water droplets and often a few ice crystals. Cloud seeding technology is based on the assumption that due to deficiency of sufficient nuclei, the clouds part with only 10% of their water content as rainfall or snowfall while the remaining moisture gets wasted away. In this case we inject chemicals to squeeze more precipitation from such clouds in which minute cloud droplets are converted into large raindrops or snowflakes, which fall on earth due to gravity.
Clouds whose tops do not reach freezing temperatures in the sky are known as "Warm clouds'"and those that extend into freezing levels upto about 13 km.into the sky are "Cold clouds"Warm clouds are seeded with hygroscopic chemicals like sodium or calcium chloride Etc.,while cold clouds are seeded with 'ice particles' or "Silver iodide particles"Etc., 3]Cloud seeding is done to definitely reduce the impacts of Climate Change as can be seen by the latest scientific article under the web site:http://www.hindu.com/2010/07/22/stories/2010072265102200.htm
SS- Classic "glaciogenic" cloud seeding is the process of introducing ice nuclei (silver iodide) into clouds composed of super cooled liquid water droplets. These droplets will then rapidly freeze into crystals and the ice will grow quickly into precipitation.
VS- What are the main benefits of cloud seeding?
TSR- Enlightened scientists, bureaucrats, industrialists and statesmen in about 50 countries have been using cloud seeding operations for over 40 years for various purposes like:
1. Increase of annual rainfall for drinking and agricultural purposes
2. Dispersal of fog in airports and metropolitan city roads
3. Increase of hydropower generation at the cheapest cost
4. Suppression of hail storms to reduce damage to life, crops and properties
5. Mitigation of devastating impacts of recurring droughts
6. Mitigation of damaging impacts of global warming and summer temperatures
7. Increase of annual rainfall for improving the forests, wildlife and the environment
VS- Will we be able to reduce pollution and control climate change with this technology?
SS- No. The process of enhancing rainfall on a small regional scale is vastly different than influencing climate change - a global phenomenon. Similarly, there's no real hope of using this approach to change local air pollution. We aren't sure why cloud seeding appears to be working so well in Tasmania, when it has failed to produce clear results in other parts of the world. It may, in part, be because the clouds are so pristine, coming off the Southern Ocean. If so, local air pollution may inhibit this glaciogenic approach.
TSR- Cloud Seeding could be useful in reducing the dust and gaseous pollutants floating in the air. It is done in China to clean the dust-laden air by the snowfall and the rainfall, which also help in cleaning the leaf surfaces plants and external faces of buildings and monuments coated with dusty air. The precipitation caused by cloud seeding adds more water to the annual flows in the rivers and their tributaries and thereby dilutes the concentration of pollutants in the flowing water to enhance their self-purification capacity. Similarly addition of water into ponds and lakes helps in dilution of pollutants and thereby make the waters useful for secondary purposes. Even ground water gets its pollution levels diluted due to augmentation of water resources by cloud seeding. Since additional water promotes tree growth and thereby the atmosphere becomes cooler the impacts of climate change can be slightly reduced.
VS- Where and how is cloud seeding used in the World?
TSR- Cloud seeding is used in about 40 countries in the world. It is used to augment water resources in rivers and lakes and to improve ground water resources. Cloud seeding is done in Snowy Mountains of Australia to augment snowfall to promote tourist trade. Cloud seeding is done in Tasmania to augment hydro-electricity production at cost benefit of 1:30. In China and Russia cloud seeding is done to provide clear skies during festive occasions like the Olympic Games and other annual celebrations.
VS- Is cloud seeding commercially interesting (farming, tourism etc.), or does it represent greater interest for governments?
SS- Here in Australia, it's commercially driven. Hydroelectric companies seek to increase rainfall into their damns and produce more electricity. Given the drought, I would think the government would be more interested, but there was a long history of government support for this in Australia.
TSR- Cloud seeding is commercially useful for agricultural operations, augmentation of Municipal water supplies and hydro-power generation, ground water replenishment and promotion of tourist trade in sky resorts. Cloud seeding is used in some cities in USA for removing fog, which interferes with traffic in the aerodromes, metropolitan city roads. Some countries like USA use cloud seeding for quenching forest fires. In view of the economic importance of additional precipitation many countries are resorting to cloud seeding operations on a large scale.
VS- There are fears of toxicity and possible soil contamination, which may be caused by cloud seeding, is it true? What does the science say?
TSR- Research investigations on the damaging impacts of chemicals used for cloud seeding indicated no perceptible damage to public health and the environment. Since the seeding materials used for the operations are very small in quantity their presence in the precipitation has been detected to be very low in concentration. Concentration of silver is much below its US Public health Standard of 50 micro-grams per litre. In the case of iodine, its presence in the rainwater sample collected at the end of cloud seeding operations is found to be far lower in concentration than that found in the common iodized table salt used by the people.
VS- What about the effectiveness of this technology, some say it is unclear whether it really works.
SS- I respect that argument. Indeed, I suspect it is true for most parts of the world. Tasmania may just be special because of the pristine Southern Ocean. But in Tasmania we've had two positive field experiments and now 45 years of seeding to get some statistically significant results.
TSR- Cloud seeding experiments were being conducted in about 40 to 50 countries for more than 4 to 5 decades. On the average the benefits are estimated at about 20 times the cost incurred for the operations. After reviewing the results of cloud seeding operations for several years the world Meteorological Organization (WMO), American Meteorological Society (AMS) and the Weather Modification Association (WMA) issued statements indicating 5% to 20% additional rainfall from clouds over the continents and 30% from the maritime clouds. It was further stated that the hail suppression experiments caused reduction of 20% to 50% in the costs of damage due to hailstorms.
VS- There are also opinions that cloud seeding can increase rainfall in one territory at the expense of another, is it true?
TSR- This usual question of whether cloud seeding “robs Peter to pay Paul” must be answered with an emphatic “no”. The cloud seeding in one place does not cause any perceptible reduction in rainfall that normally occurs in the neighbouring areas. Out of the total atmospheric moisture continuously flowing over any region the normal condensation removes about 20% of the total moisture to form into clouds. Cloud seeding causes additional precipitation although a cloud normally gives 20% of its moisture as rainfall. Further artificial rain making by cloud seeding causes additional precipitation of 20%. So 100 (0.20 x 0.20 x0.20)=0.8% of the water vapour is removed.
VS- Does this technology have a future, if yes where will it be widely used?
SS: In the present form, it has a limited future. However it's possible that modifications can make cloud seeding more effective and viable in other locations.
VS- What are the major steps to overcome today to make this technology really useful and widely developed?
TSR- Cloud seeding is opposed by some scientists, bureaucrats and politicians due to lack of sufficient level of awareness about the subject. Sometimes scientists may pursue their own interests and development of technology such as cloud seeding suffers. In order to overcome the opposition from such vested interest among scientists, bureaucrats and politicians who live at the expense of public sufferings we have to create large scale awareness among the school, college and the university students, Government Officials and general public on the scientific foundations, technological feasibility, economic viability and social acceptability of cloud seeding operations for promoting public health, environmental resources, National economy and sustainable development.
SS- One of the aims should be getting cloud seeding work in more marginal conditions. This may require a lot more insight and a rethink of the basic concepts and approaches.
VS- Prof. T. Shivaji and Prof. Siems, thank you very much for your contributions to this article.
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WIND MOVEMENTS AND CLOUDS
Why do most of the clouds move from south to north direction over our subcontinent?
Mulanur, Tamil Nadu
Clouds usually move according to the wind pattern. Wind is caused due to difference in temperatures and pressures which may be affected by various factors. Movement of wind is a very complex phenomenon affected by latitude, proximity of water bodies, sea shore and land undulations. It is also affected by the rotation of the Earth.
Wind blows from points of high pressures to low pressure points. Wind caused due to difference in temperatures is known as convection current. Wind moves from warmer regions near the Earth surface to higher up colder regions. Where the land mass is surrounded by sea water, air near land surface is warmer and moves up. To replace the air mass, wind blows from sea to the land mass. This is also known as breeze. Then there is global movement of wind.
Earth regions near the equator get maximum heat energy from the sun. This causes air to rise up vertically near the equator. To replace, cold wind blows from higher latitude regions. There are also seasonal variations in the direction of wind due to tilt of the Earth, which further makes the phenomenon more complex.
In our subcontinent, the southern regions are surrounded by sea water which causes the wind to move from sea to the land mass i.e. from south to north. The direction changes as the seasons change.
Greater Noida, Uttar Pradesh