Title: The Science of Cloud Seeding
1The Science of Cloud Seeding
Students Seminar Series 13th October
2003 .by, Vinoj V PhD Student CAOS, IISc
2Background
- By the year 2025 two thirds of the world
population will live under severe water stress
conditions as determined by studies of the World
Meteorological Organization (WMO) - The rapid growth of Agricultural and Industrial
sector along with the population explosion makes
India particularly vulnerable. - Though India get high amount of rainfall compared
to many other countries, the large
infrastructure and water intensive agricultural
practice makes India vulnerable to even to the
minor swings (lt 5) in rainfall - Water related problems within the states
- India is at its absolute water limits (Bryson.,
1989)
3Mitigation
- Intelligent Utilization of the available Water
Resources - Rainwater Harvesting
- New source of water?
- Artificial Rain Making! - Cloud Seeding?
- Remember Atmospheric Vapor is only 0.001 of the
total water in the hydrosphere
4American Indians
- The rain dance was a big part of American Indian
culture and helped them carry on with their day
to day activities. - They believe by pleasing the rain god he would
provide rain for their crops.
5American Indians
- Each tribe had a different god or ceremony for
their rain needs. - The tribes were similar in the fact that each one
of them relied on rhythmic dancing in their
events. (http//users.rowan.edu/)
6- According to Rig Veda - The earliest accepted
Gods were - DYAUSH PITA (the sky father)
- PRITHVI MATHA (the earth mother)
- VAYU (the wind God)
- PARJANYA (the rain God)
- SURYA (the sun God)
- VARUNA (the God of oceans)
- AGNI (the fire God)
- INDRA (the war God)
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8The Cloud Formation
- Homogeneous nucleation of Water droplets require
high Degree of super saturation (350-400) - Heterogeneous nucleation in the presence of Cloud
Condensation Nuclei (CCN) - Two important processes on how rain is produced
- Collision-Coalescence Process
- Ice-crystal (or Bergeron) process
9Droplet Growth
Typical Cold Clouds
Warm Clouds - Collision and
Coalescence Cold Clouds - Ice Crystal
Process
Typical warm Clouds
10Seeding Definition
- The deliberate treatment of certain clouds or
cloud systems with the intent of affecting the
precipitation process(es) within those clouds. - Borrowed from Physical Chemists,
- A method used to precipitate solute from the
solvent - Pieces of solid material placed in a
supersaturated solution to promote precipitation
of the dissolved solute
11The Beginning
- Cloud seeding began by dropping dust particles in
to the cloud to help the water condense. - The dust was ejected from crop dusting planes
which were already outfitted for the job. - There are now more scientific ways to cloud seed.
12The Beginning
13Cloud Seeding
- Cloud seeding is actually a very complex process.
In the simplest terms, it introduces other
particles (CCNs) into a cloud to serve as cloud
condensation nuclei and aid in the formation of
precipitation. - There are three types of cloud seeding static
mode, dynamic mode, and hygroscopic seeding. - Static mode cloud seeding seeks to increase
rainfall by adding ice crystals (usually in the
form of silver iodide or dry ice) to cold clouds.
- Dynamic mode cloud seeding increases rainfall by
enhancing "vertical air currents in clouds and
thereby vertically process more water through the
clouds." Basically, in this method of seeding, a
much larger number of ice crystals are added to
the cloud than in the static mode. - In hygroscopic seeding, salt crystals are
released into a cloud. These particles grow until
they are large enough to cause precipitation to
form. Clouds can be seeded from above with the
help of airplanes that drop pyrotechnics, or from
the ground by using artillery or ground-to-air
rockets
14The Seeding Concepts
Static Seeding Alter the microphysical
Properties of clouds
Dynamic Seeding Attempt to modify the Air
motion within the clouds
Hygroscopic Seeding Use of hygroscopic material
to Obtain the intended result (eg salt) Static
or Dynamic
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16- Warm Cloud Seeding
- Formation of Rain through Hygroscopic Seeding
- Hygroscopic Particles
- Extremely moisture absorbent
- Grow in low humidity air below cloud base
- Examples of Hygroscopic Material
- Common Table Salt
- Ammonium Nitrate Urea Fertilizer
- Objective of Hygroscopic Seeding
- Introduce large drops into cloud
- Large drops collide with small cloud droplets
and grow into rain drops (Coalescence) - Rain drops heavy and large enough to fall out of
cloud and reach ground.
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18Mixed Clouds
19Seeding Materials
- The materials used in cloud seeding include two
primary categories, tied to the type of
precipitation process involved - Glaciogenic (ice-forming) Silver iodide, dry ice
and compressed liquid propane - The second major category is focused on cloud
systems where the warm (coalescence) process
predominates. - Hygroscopic (water attracting) materials such as
salt, urea and ammonium nitrate can be utilized.
Of the hygroscopic materials, the most commonly
used are salts.
20Silver Iodide
- Why Silver Iodide ?
- It has a crystalline structure similar to ice
crystal, and it acts as an effective ice nucleus
at temp. of -4C and lower - Silver iodide, when burned, creates extra ice
crystals in winter clouds to increase snow fall.
(The first AgI generator could discharge 1016
particles per gram) - (www.wmi.cban.com/)
- It can be distributed from the ground...
21Silver Iodide
22Automated High-Output Ground Seeding System
Aircraft-mounted flares
Cloud Seeding Aircraft
23How Cloud Seeding Works
24How Cloud Seeding works?
- In cold cloud seeding.,
- the introduction of an ice-forming nucleating
agent, (e.g., silver iodide) causes supercooled
liquid water droplets to freeze. Once these
droplets freeze, the initial ice embryos grow at
the expense of the water droplets around them. - The first freezing process is often referred to
as a static seeding effect, increasing the
efficiency of the precipitation process within
the seeded cloud volume. - The second freezing process, resulting from
release of additional heat into the cloud, is
often called the dynamic effect, whereby the
treated clouds are invigorated, thus processing
more moisture.
25 Warm Cloud Seeding at 2 to 3 km heights
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27Cold Cloud Seeding
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32Indian Experiment
- IITM, Pune was involved in cloud seeding
experiment for a period of 11 years in the
seventies - Reported Increase in rainfall due to seeding
-
24 - Different states have their own operational
programs whose success is still being debated
33Interesting Applications
- Hail suppression
- Hurricane Modification
- Eg Operation STORMFURY
- Fog Dispersion
- Defence Applications
34Suppression of Hail
- Cloud seeding can be used to cause rain instead
of hail. - However suppressing hail in one area often causes
more in another. (twri.tamu.edu)
35Thank You