GROUND GENERATORS FOR CLOUD SEEDING
Director, Centre for Environmental Studies, GITAM Institute of Science, GITAM University
Director, Centre for Environmental Studies, GITAM Institute of Science, GITAM University
[excellent review of cloud seeding work in china by Tao,expert,2005]
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
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
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
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,
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
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
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
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.
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.
The parameters required for this experiment are: humidity must be more than 70%,
wind velocity about 15kms per hour, cloud thickness must be about 10,000ft. 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 1200o C 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
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
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