Director, Centre for Environmental Studies,
Gitam University, Visakhapatnam-530 045
Cloud seeding operations are conducted successfully for almost 50 years in several countries including USA where at present 100 catchments are subjected to cloud seeding to increase winter precipitation and the increased run-off varies from 5% to 15%. 20 years of cloud seeding in Tasmania has been proclaimed as a successful operation by the Australian Council of Scientific and Industrial Research Organization (CSIRO) which confirmed that the rainfall can be increased by 15% to 20% on seeded days. Due to lack of adequate water resources for drinking, agriculture, industry and other needs cloud seeding operations have been taken up in Jordan since 1986 under Precipitation Enhancement Project (PEP). Some of the salient features of this project are:
A special airplane for cloud seeding and 24 ground generators, located at selected sites are used.
● AgI is used with acetone solution
● The average time of cloud seeding by the Airplane is 50-70 hours/season.
● The average of the cloud seeding by the ground generators is 2000 hours/season
● The Doppler C-band weather radar determines the candidate cloud that could be seeded
● A special GPS system is used to display the track of the airplane on the radar display.
● Voice communication is available between the radar meteorologist and the airplane to
direct the pilot to the candidate clouds.
In China the experts are using not only many aeroplanes but are also using many ground generators including rockets, cartridges and anti-aircraft guns for cloud seeding. However since the use of rockets and anti-aircraft guns pose some problems and since aeroplanes cannot be used in certain special locations like deep valleys surrounded by steep hills the ground generators become the choicest instruments for cloud seeding to augment precipitation in some localities.
The latest in ground-based pyrotechnic applications are the ground-based flare-trees offered by the Weather Modification Company of USA . This flare-tree has a tripod base which provides good stability even under the most extreme weather conditions and provides for easy leveling. The flare-tree is provided with 9 racks, each holding upto 12 glaciogenic or hygroscopic flares and it can be configured for manual or remote controlled operation. Some kinds of ground generators are trailer-mounted so that they can be positioned prior to the operation in the selected locality and removed conveniently after completion of the work. In case these generators are to be used on the mountains, they would be located near the existing roads or access tracks and below ridges to minimise visibility. The trailers are camouflaged steel containers having a gas burner located 3 meters above the ground. Propane gas from an adjacent 2000 litre container vaporizes a mixture of silver iodide and acetone. The combustion and the resultant plumes are generally invisible. Different kinds of ground generators can be developed and used for different localities. Some of the Indian farmers in Kutch region of Gujarat previously used locally developed ground generators and conducted cloud seeding experiments. Many western experts also developed different ground generators for cloud seeding operations. These case studies are presented here.
I. Extensive use of ground generators in USA :
In several states of USA the North American Weather Consultants (NAWC) have conducted cloud seeding operations in several dozens of localities by using not only aeroplanes but also many advanced ground generators as listed at the end of this presentation. In order to unfold the detailed procedures followed in using ground generators some of the salient features of one of the field projects executed by the North American Weather Consultants (NAWC) under the guidance of the reputed International expert Dr.Don.A.Griffith is presented here with his kind permission.
Gunnison Precipitation project Cloud seeding Operational Plan :
Objectives of the Project: The objective of the proposed project is to augment the precipitation/
snow pack that occurs with the passage of late fall, winter and spring cloud formations over the intended target areas in Gunnison river, a tributary of Colorado river in USA;
The primary target area is defined as those mountainous areas above 9000 feet above the mean sea level msl located in southwestern Gunnison County, northern Hinsdale and northern Saguache Counties. The proposed target area constitutes most of the tributaries to the upper Gunnison River Drainage that enter the Gunnison River from the south. Figure 1 provides a map of the proposed primary target area.
There will be some positive (increases in precipitation) effects downwind of this primary target area. These effects will occur primarily on the Eastern slopes of the Sawatch Range and Southern slopes of the La Garita Mountains.
Project Implementation: Operational seeding decisions of when and which ground based generators should be utilized during specific cloud system occurrences will be made by the Company headquarters which is equipped with four personal computers with T-1 access to the internet. A variety of weather products, available through the internet, will be monitored to assist in making these seeding decisions. These products, most of which are provided by the National Weather Service (NWS) will include: weather satellite (IR and visual) photos, surface charts, constant pressure charts (i.e.700,500mb), upper-air rawinsonde observations (weather balloons), NEXRAD weather radar information, surface weather reports (typically available at hourly intervals), NWS weather forecasts and prognostic (forecast) charts of a variety of weather parameters.
NAWC meteorologists will monitor the above information to determine if NAWC’s generalized cloud seeding criteria are met and, if so, which generators should be operated. NAWC’s generalized seeding criteria developed upon practical considerations plus the results from previous winter orographic weather modification research programs are presented below.
NAWC Winter Cloud Seeding Criteria :
(1) cloud bases are below the mountain barrier crest.
(2) low-level wind directions and speeds that would favor the movement of the silver iodide
particles from their release points into the intended target area.
(3) no low level atmospheric inversions or stable layers that would restrict the vertical
movement of the silver iodide particles from the surface to at least. The -5°C (23°F) level
(4) temperature at mountain barrier crest height expected to be -5°C (23°F) or colder
(5) temperature at the 700 mb level (approximately 10,000 feet) expected to be warmer than
A network of 8 to12 ground based silver iodide generators will be used in the conduct of this project. These generators will be sited at private residences or public places of business. The residents or business operators will be trained in the operational procedures to be used in turning the generators on or off.
NAWC meteorologists will contact these operators when conditions have been determined to be favorable for operations and request that the generators be turned on. When conditions are no longer favorable, the operators will be called to turn the generators off. Figure 1 provides tentative locations of these generators. The project is planned to operate during the period of November 15th – April 15th during the next five winter seasons beginning in the 2003-2004 winter season. This period is the same as that contained in an existing cloud seeding permit covering most of the remainder of the upper Gunnison River Drainage.
Figure 2 provides a photograph of one of NAWC’s ground based, manually operated units. Each generator site is equipped with a propane tank. The propane is lit within the generators burn chamber and then the silver iodide (dissolved in acetone) is injected into the propane flame. As the effluent from the generator cools, literally trillions of microscopic sized particles of silver iodide are produced. These particles have the ability to cause water droplets within clouds that are colder than approximately -5oC to freeze. The tiny ice crystal that is produced, if it remains in a favorable environment, will grow into a snow flake. NAWC will use a seeding solution composed of acetone, silver iodide, sodium iodide and paradichlorobenzene. This solution has been shown to produce more effective seeding particles at warmer temperatures (i.e. about -10o to -5oC and to produce these crystals more quickly than pure silver iodide (Finnegan, 1999). Each generator will consume 8-12 grams of silver iodide per hour of operation. Aerial seeding is not proposed for this project.
Project Design for Economic Benefit to the Target Area: The proposed project design is based upon NAWC’s significant experience in designing, conducting and evaluating similar winter orographic weather modification projects in the western United States dating back to the 1950’s. The design is also based upon the conduct of a number of research programs in weather modification including the Climax Experiments I and II conducted in the Central Rocky Mountains of Colorado ( Mielke, et al, 1981) and the Colorado River Basin Pilot Project (CRBPP) conducted in the San Juan Mountains of south-western Colorado. NAWC’s former affiliate company, Aerometric Research, performed a comprehensive evaluation of the latter program (Elliott, et al, 1976).
Evaluations of previous NAWC winter orographic projects have indicated increases in target area precipitation in the range of 10-20%. For example, a long term project that began in central and southern Utah in 1974 and continues to the present time has produced approximately a 14% increases in target area precipitation based upon a target and control evaluation (Griffith, et al, 1991). Results from other projects conducted in Utah and surrounding Inter-Mountain states are provided in Figures 3 and 4.
Based upon the positive results achieved in these projects and also upon the topography of the target area and the type of storms that frequently impact the area, it is NAWC’s expectation that a 10-20% increase in target area precipitation can be produced by this project.
The predicted 10-20% increases will have a variety of positive impacts within Gunnison County. The additional snow in the winter and spring months will benefit the tourism interests (i.e. skiing, snowmobiling).
A report prepared by the Colorado Department of Natural Resources documents the impact of additional snow on ski area attendance (Sherretz and Loehr, 1983). This report estimated that a 15% in snowfall for hypothetical dry winters at Colorado ski areas are associated with 2-8% increases in total season visits.
Increases in winter snow pack will result in enhanced spring and summer stream flow on the upper Gunnison River and its tributaries. This additional stream flow will provide an economic benefit to a variety of users and consumers. User groups that may derive benefits will include: hydro-electric generation facilities, fishing, rafting and general tourism interests. User groups that will benefit from the project will include irrigated agriculture, livestock and municipal water interests. (Fig-1)
A report prepared by the Utah Division of Water Resources estimated that the additional streamflow that results from a large winter orographic weather modification program being operated in the State of Utah by NAWC is being produced for approximately $1.02 per acre foot (Stauffer, 2001). The value of this water, depending upon its use, is probably in the range of $10-$50 per acre foot in primary benefits. There are a number of secondary benefits as well, for example the impacts on tourism, which increases the value of this water. Increases in tourism also generate additional sales tax revenues which will benefit Gunnison County and the State of Colorado.
Benefit to Both in the Target Area and Colorado Countries: The expected economic benefits to Gunnison County were documented in the previous section. There will be additional general benefits including increases in timber growth, increases in water stored in under-ground aquifers, increased spring flows, and carry-over storage in reservoirs from one year to another which may lessen the impacts of future droughts in the area.
Some of the additional water generated by the project will flow downstream into other Colorado counties (e.g. Montrose, Delta, Pitkin, and Chaffee Counties) which will derive economic and general benefits from this additional water (i.e. irrigation, hydro-electric generation, municipal water, tourism). Surrounding counties will also benefit from increased tourism in the area which will generate additional tax revenue for these counties and the State of Colorado.
Project is Scientifically and Technically Feasible: A Policy Statement on Planned and Inadvertent Weather Modification adopted by the American Meteorological Society in 1998 (AMS, 1998) which states in part “There is statistical evidence that precipitation from supercooled orographic clouds (clouds that develop over mountains) has been seasonably increased by about 10%. The physical cause-and-effect relationships, however, have not been fully documented. Nevertheless, the potential for such increases is supported by field measurements and numerical model simulations.” NAWC’s design for this project is directed at winter supercooled orographic clouds. This AMS statement provides scientific support to NAWC’s design. This policy statement was no doubt based in part upon earlier research programs conducted in Colorado that were referenced earlier (Climax I and II and the Colorado River Basin Pilot Project). Another research program of relevance to the design of this project was conducted in the Jemez and Sierra Nacimiento Mountains of northern New Mexico from 1969 to 1972. This project utilized ground based portable silver iodide generators to seed portions of winter orographic storms on a randomized basis. A statistical analysis of the effects of the seeding indicated an increase of 13% during the seeded 24 hour periods (Keyes, et al, 1972).
NAWC cites its long history, which dates back to 1951, in conducting successful winter orographic weather modification programs as evidence that the conduct of this project is technically feasible. Attachment provides a summary listing of some of NAWC’s previous operational precipitation enhancement projects. Many of these projects were winter orographic weather modification projects. (Table-1)
For more details refer the websites :
II. Indian farmers seed clouds with ground generators :
As a social worker of Kutch Mr.Shanthilalbhai Meckoni realised that the development of the Kutch region of Gujarat can not be achieved unless the annual rainfall of the region amounting to about 250mm is substantially increased for providing adequate water for drinking and irrigation purposes. In order to conserve water he implemented several water harvesting structures as Vice-President of Vivekananda Research and Training Institute in Kutch region. In the process he realised that the utility of his water harvesting structures becomes more useful if only he can increase the annual rainfall by tapping the sky water from the clouds whenever they appear in the sky over the Kutch region.
He discussed with several foreign experts on how to conduct cloud seeding experiments to make available more water for the domestic and agricultural needs of the people in this region. Among the experts he contacted one professor from Jerusalem University told him how they conducted cloud seeding experiments by using ground generators in Israel for augmenting the annual rainfall. Israel used hot air ovens packed with coke that was heated upto about 1200oC for sprinkling technical grade silver iodide powder in small quantities so that the vaporized fumes directly get into the super cooled regions of the cloud where the silver iodide particles work as ice particles over which the super cooled water and the moisture are precipitated to promote the growth of ice particles into ice crystals and then to ice flakes that fall down to earth due to gravity as snowfall or rainfall.
Meckoni considered the special topographical and meteorological features of his region and made suitable modifications in the procedures for conducting the cloud seeding experiments on the lines of the initial cloud seeding experiments conducted in Israel. The farmers in the Kutch region of Gujarat came forward to take advantage of this new technology to improve their lot. Meckoni has supplied the farmers with the ovens fixed with the blowers along with the coke and technical grade silver iodide needed for conducting the experiments. The farmers used to look into the skies for the arrival of dark clouds and cloud clusters and then immediately start the experiments for seeding such suitable clouds. They used to sprinkle 200 gms of silver iodide over hot coke oven with 1200oC at 5 to 8 grams at a time for 40 minutes by using a tea spoon. They used to maintain proper temperature so that the silver iodide sprinkled over the white hot coke in the oven does not get into the liquid state but gets directly into the vapour state so that the vapours directly get carried by the updrafts into the colder regions of the clouds in about half an hour time. Heavy rain used to fall on the ground within 45 minutes. The base of the clouds must be within 1km to 1.5km from the ground level because if the cloud base is far higher from the ground the precipitation from the clouds may not reach the ground as rainfall as the droplets may be carried away again as moisture into the atmosphere.
The farmers received scientific information about the suitability of clouds and the timings when they have to conduct the experiments. The officers of the Indian Meteorological Department who were operating weather radars in Gujarat used to detect the appropriate clouds and pass on the information through the All India Radio station to the farmers who in turn used to take timely action to conduct the experiments. The farmers also used to confirm by local observations about the seedability conditions before launching the experimental operations. The farmers are said to have come forward to collect donations from each village for purchase of chemicals and equipment for the experiments and succeeded in achieving their goals of augmenting the annual rainfall in the drought prone Kutch region. However this good work didnot continue for long for various reasons.
Taking this example the farmers in other states must develop improved ground generators and conduct these cloud seeding experiments to augment their annual rainfall. It must be remembered that ground generators are used in several countries for cloud seeding operations to augment the snowfall or rainfall.
Even if the state Government uses aeroplanes regularly for cloud seeding operations it may not be possible for the aircrafts to seed all the clouds at a time when suitable clouds are likely to be present in distant places in the state under highly favourable weather conditions. For various reasons, the pilots may not be able to reach the target clouds within an hour or the life time of the clouds, making the operations ineffective Thus ground generators, anti-aircraft guns and rockets are still used for cloud seeding operations mostly in several parts of China and Russian states. The Indian farmers also must make genuine attempts to increase the annual rainfall in their respective regions by conducting cloud seeding operations by using suitably modified ground generators.
A smoke generator emits 1016 smoke particles per gram of AgI burned and only one in 10 of these particles are effective as ice forming nuclei at –20oC while only one in one lakh at –10oC with a consumption rate of a few grams of AgI per hour. The generator effluent at 10 meters downwind of the generator will have nuclei effective at –20oC of about 3 x1011 crystals per cubic meter. Of those effective at –10oC the concentration will be 3x107 per m3. It means the effluent would over-seed the cloud near the generator. But if the generator is located at a point at the base of the mountain slope or in a low flying aeroplane about 1km below the –5oC level entrained within convective updraft, the smoke will be diluted by turbulence by a factor of 100 to one million times. On a complex mountain terrain the generator smoke rises and spreads rapidly and the plume top was found to rise 1.5kms at 5km downwind in the CLIMAX project in wind tunnel modelling.
III.Mini-Rockets Developed by Dr.J.V.M.Naidu and Prof.T.Shivaji Rao for use as Ground Generators
With the assistance of M/s.Sitaramaiah Fire Works of Anakapalle,Dr.J.V.M.naidu and Prof.Shivaji Rao have
developed Mini-rockets for use as ground-generators[see picture above]The Black Powder used as rocket fuel for explosion purposes usually contains 75% saltpetre[KNO3]10% Sulphur and 15% Carbon..The Nitrate supplies the reaction with the required Oxygen while the Charcoal supplies the fuel for the reaction as a source of Carbon and the Sulphur works as a fuel that lowers ignition Temperature and helps to increase the speed of combustion.
These materials are used in different proportions,such as,5:1:1, 7:2:1, 6:2:1,9:3:1 and also 15:3:2 as required.
The Chemical reaction occurs probably as : 10 KNO3+3S+8C =2K2CO3+3K2SO4+6CO2+5N2
The materials like common salt powder are packed as shown in the figure for attachment to the mini-rocket.
For ground generators,small flower pots are packed with the fuel by inserting Silver idoide technical grade powder in the centre so that when it is ignited on elevated places,the smoke is emitted and it gets into the cold clouds.
These methods were successfully employed for augmenting precipitation to fill Yeleru reservoir during August,2005
An English Daily Bombay Times, in its Edition dt.23-6-1995 presented the successful artificial rain making experiments conducted by Shantilal Meckoni who successfully produced additional rainfall in Kutch region of Gujarat and in the Vaitarna and Tansa drinking water lakes of Bombay by sprinkling silver iodide over hot coke oven in ground generators. This rain induction method involves placing silver iodide powder in a furnace to evaporate upwards into supercooled water regions in the clouds where the supercooled water forms into ice crystals that grow into ice flakes which fall down to earth as heavy rainfall.
pre-conditions required for a successful experiment are: humidity must be more than 70%, wind velocity about 15kms per hour, cloud thickness must be about 10,000ft.[3 km.] and temperature in the cloud should be minus 5o C.
The experiment conducted at Tansa lake produced more than 70mm rain in 2 hours duration. For each experiment just 250gms of silver iodide and a small amount of coke for the furnace is needed to maintain a temperature of about 1200oC and a blower is used for the purpose. Meckoni says that Israil and Russian Governments conduct these experiments even when there is natural rainfall because they want to increase the water availability by making the clouds grow in size by merging with the neighbouring smaller clouds and also by processing more moisture from the updrafts created by the latent heat released during the experiments. There are no side effects as the iodide in the rain water disintegrates and the silver remains only in very miniscule quantities that are within the safe limits. Meckoni learnt this science of rain induction from a visiting professor from Jerusalem University and chose Kutch his homeland for these experiments.
According to a report prepared by Bombay Municipal Corporation from July 16, 1992 to August 9, 1992 cloud seeding work was carried out for 9 days at Tansa and Modak Sagar lakes. On these days it was observed that the average rainfall was about 25mm per day at Tansa and about 35mm per day at Modak Sagar while the average rainfall recorded when no cloud seeding was done was about 10mm per day at Tansa and about 13mm per day at Modak Sagar. It means that there was a 200% increase in the rainfall during the cloud seeding days. It is reported that the water level in Vaitarani lake rose by 3 meters in 2 days around 25 July 1992. It is a very inexpensive technique because for one station of 5000 hectares the Bombay Corporation spent Rs.2,250/-
Operational Experimental Conditions : To summarise, the humidity should be over 70%. The cloud should be at a height of 10,000 feet the atmospheric temperature of the cloud should be minus 5oC, 250gms of silver iodide should give best results and the wind velocity should be less than 15km/hour. For more information on warm cloud seeding experiments conducted with the help of the ground generators please see the chapter on “Cloud seeding experiments in India”.