CLOUD SEEDING what and why?

CLOUD SEEDING what and why?


Every cloud has a silver lining. One of the elements of nature and the basic need of human life to survive on this blue planet is water. Water as time passed became a scarce resource and we have started looking skywards for relief. The sight of a dark cloud in the horizon of a summer sky most definitely would bring on a smile, as the cloud is the beginning of the hope that it might bring with it a shower to cool the temperatures down. More so when this is a cloud that is spotted in a drought effected area, where the only source of water is if the gods above so decide.

All of us know what a cloud is. But the concept of cloud seeding does conjure images of someone up in the sky planting seeds of clouds. Cloud seeding in its basic form is the method of weather modification. The uses of cloud seeding can be used to increase precipitation. First we need to understand how clouds are formed and how precipitation takes place.
Warm air that rises from above earth’s surface cool down into droplets of water which are the smallest component of a cloud. These droplets contain dust, salt, or soil present in the atmosphere, called cloud droplets, which group together to form a large cloud. Cloud precipitation can happen in any one of the two ways. During the warmer temperatures millions of cloud droplets join to form a single droplet in a cloud and during cooler temperatures the same droplets from crystals of ice which when heavy or large fall back on to the ground as rain, snow, or hail.
The complex process of cloud seeding can be explained in a simple way as introduction of other particles into a cloud to enhance condensation and precipitation. The three methods of cloud seeding are static mode, dynamic mode, and hygroscopic seeding.
In the static mode of cloud seeding rainfall is created by adding silver iodide or dry ice to cold clouds. Vertical air currents are enhanced in the dynamic mode whereby heavier clouds are harvested as much larger number of ice crystals are used than in the static mode. Releasing of salt crystals is called hygroscopic seeding, this is done with the help of airplanes or through rockets launched from the ground.
Why cloud seeding[1]:
From scientific community point of view, as only a small part of the available moisture in clouds is transformed into precipitation that reaches the surface, what this mean is that scientists and engineers could explore more possibilities of augmenting water supplies by means of cloud seeding. If more water could be transformed into precipitation, the potential benefits appear very attractive.
However, there has been a lot of debate about the effectiveness of this form of inducing rain. First and foremost people see this as man’s intervention of nature. Many see it as stealing of rain from another area. All this debate has led to quite a few arguments as to the boundaries of cloud seeding and weather tampering. People argue that it is difficult to measure the amount of natural precipitation when it is orchestrated.
However, there is clinching evidence from the scientific community that supports this methodology especially that of winter cloud seeding in hilly areas when compared to warmer counterparts. Societies like the Weather Modification Association, World Meteorological Association, and American Meteorological Society affirm the same.
History behind those clouds
The seeds of this method of cloud harvesting were sown by a scientist Irving Langmuir and the first such attempts were made in Massachusetts in 1946. Scientist Bernard Vonnegut takes the credit for using silver iodide in cloud seeding. Silver iodide and carbon dioxide ice is used to start winter snowfall and to stop hail.
The first organization that start cloud seeding in a commercial way was Irving P. Crick and Associates of Palm Springs[2], California in 1970 and the contract work for the Oklahoma State University in 1972 was conducted to increase the dying water resources of Stillwater lake in Oklahoma. The most successful of the experiments was conducted in Snowy Mountains.
The forerunner in this field is China, which increases rainfall in its driest regions through cloud seeding. Increased usage of this method by China has subjected it to much criticism from neighboring countries which soon realized that China’s gain was their loss.
Cloud seeding in India
After much thought, the Southern Indian states like Karnataka and Andhra Pradesh have tried to test cloud-seeding operations for rains in drought-hit areas. After almost 55 years what started as an experiment is giving meaningful commercial results thus increasing the viability of using this procedure to augment rain.
In Karnataka, “Project Varuna” was launched in September 2003. According to the official reports, this operation achieved almost 95% success. An average rainfall of 50-70 mm was observed and recorded in Haveri, Gadag, Bagalkot, Bijapur, Koppal, Raichur, Gulbarga and Bellary districts.
In Andhra Pradesh: Faced with erratic rainfall in the decade gone, by Andhra Pradesh government on July 21, 2004, launched cloud-seeding operations in 10 of the state's districts. This was carried on for a period of 105 days. The state government has engaged aircrafts from Banagalore and the selected districts of Anantapur, Chittoor, Cuddapah and Kurnool in Rayalaseema, Mahbubnagar, Nalgonda and Rangareddy in Telangana and Guntur, Prakasam and Nellore received artificial rain. This project was named “Project Varuna” with a planned outlay of Rs.12 crores. In Andhra Pradesh also, this experiment resulted in moderate success with about 50-70 mm rainfall observed in
Boon or ban?
Theoretically, "cloud seeding" can work only for clouds containing super-cooled water droplets (i.e. in a metastable condition) by initiating ice nucleation. But even without cloud seeding this may happen...may be at a different time and place. Should humans intervene to decide the time and place, as it could be a highly sensitive issue? We can, therefore, never be sure if cloud seeding will work because clouds in meta-stable condition can always result in a rainfall with or without cloud seeding. The large investment thus could go futile. It is also not a proven fact that cloud seeding is a success. It is strongly debated and there is a growing suspicion among people about it. To add more, there is no evidence to support that Silver Iodide is a nontoxic chemical. It is likely to be toxic when ingested. A wide-scale use may make it evident. Silver ions can be very toxic to small for life forms and can get concentrated in plants.
Commercial use:
Cloud seeding is also used in some instances to reduce the size of hailstones (Small pellet of ice that falls during a hailstorm), and to reduce the amount of fog in and around airports. Cloud seeding is also occasionally used by major ski resorts to induce snow fall.
Will it work???
It would be too early to predict the future outcomes of cloud seeding. However, with the available and observed data, it could be concluded that cloud seeding would work only if there are suitable rain-bearing clouds in the region. The energy involved in weather systems is so large that it is impossible to create artificially rainstorms or to alter wind patterns to bring water vapor into a region," pointed out the executive council of the World Meteorological Organization (WMO) at its meeting a few years ago[3]. There is still no convincing scientific proof of the efficacy of intentional weather modification efforts," concluded a committee appointed by the U.S. National Research Council (NRC) in a recent report. In some instances there were strong indications of induced changes, but this evidence had not been subjected to tests of significance and reproducibility.
To establish credibility of cloud seeding, a lot more scientific research and observation would be needed. Also, funding from state and central governments and other scientific research agency would certainly be a boost to this endeavor.
[1] Source: http://www.rap.ucar.edu, http://newsimg.bbc.co.uk/media/images/40383000/gif/_40383115_cloud_seeding203.gif
[2] http://en.wikipedia.org/wiki/Cloud_seeding
[3] Source: www.wmo.ch/web/arep/wmp/STATEMENTS