Cloud seed

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Cloud seed

  1. 1. The Science of CloudThe Science of Cloud SeedingSeeding Students Seminar Series 13th October 2003 .by, Vinoj V PhD Student CAOS, IISc
  2. 2. Background  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 (< 5%) in rainfall  Water related problems within the states  India is at its absolute water limits (Bryson., 1989)
  3. 3. Mitigation  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
  4. 4. American 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.
  5. 5. American 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/http://users.rowan.edu/)
  6. 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)… Indians
  7. 7. The 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
  8. 8. Droplet Growth Warm Clouds - Collision and Coalescence Cold Clouds - Ice Crystal Process Typical Cold Clouds Typical warm Clouds
  9. 9. Seeding – 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”
  10. 10. The BeginningThe Beginning  Cloud seeding began by dropping dust particles in toCloud seeding began by dropping dust particles in to the cloud to help the water condense.the cloud to help the water condense.  The dust was ejected from crop dusting planes whichThe dust was ejected from crop dusting planes which were already outfitted for the job.were already outfitted for the job.  There are now more scientific ways to cloud seed.There are now more scientific ways to cloud seed.
  11. 11.  In 1946, Vincent Schaefer (GE) - a small piece of solid carbon dioxide (dry ice) can generate a large number of ice crystals in a laboratory-generated super-cooled fog.  He then dropped about 1.5 kg of crushed dry ice into super- cooled stratocumulus clouds over western Massachusetts and found that snow crystals did indeed fall out from the cloud.  In the following year Bernard Vonnegut (GE) found that particles of silver iodide can also generate large numbers of ice crystals if the cloud is cold enough.  Seeding causes a large number of small supercooled droplets to condense onto a smaller number of seed crystals. When the seeding works correctly, the grown crystals will fall out as snow and rain, leaving a clear space behind. For the technique to work, the seed material must cause large numbers of ice crystals to form. The Beginning
  12. 12. Cloud SeedingCloud Seeding  Cloud seedingCloud seeding is actually a very complex process. In the simplestis actually a very complex process. In the simplest terms, it introduces other particles (CCN’s) into a cloud to serve asterms, it introduces other particles (CCN’s) into a cloud to serve as cloud condensation nuclei and aid in the formation of precipitation.cloud condensation nuclei and aid in the formation of precipitation. There are three types of cloud seeding: static mode, dynamic mode, andThere are three types of cloud seeding: static mode, dynamic mode, and hygroscopic seeding.hygroscopic seeding.  Static modeStatic mode cloud seeding seeks to increase rainfall by adding icecloud seeding seeks to increase rainfall by adding ice crystals (usually in the form of silver iodide or dry ice) to cold clouds.crystals (usually in the form of silver iodide or dry ice) to cold clouds.  Dynamic modeDynamic mode cloud seeding increases rainfall by enhancing "verticalcloud seeding increases rainfall by enhancing "vertical air currents in clouds and thereby vertically process more water throughair currents in clouds and thereby vertically process more water through the clouds." Basically, in this method of seeding, a much larger numberthe clouds." Basically, in this method of seeding, a much larger number of ice crystals are added to the cloud than in the static mode.of ice crystals are added to the cloud than in the static mode.  InIn hygroscopic seedinghygroscopic seeding, salt crystals are released into a cloud. These, salt crystals are released into a cloud. These particles grow until they are large enough to cause precipitation to form.particles grow until they are large enough to cause precipitation to form. Clouds can be seeded from above with the help of airplanes that dropClouds can be seeded from above with the help of airplanes that drop pyrotechnics, or from the ground by using artillery or ground-to-airpyrotechnics, or from the ground by using artillery or ground-to-air rocketsrockets
  13. 13. The 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
  14. 14. Cloud Seeding Warm Cloud Seeding Cold Cloud Seeding Glaciogenic Seeding Cumulus Clouds having cloud top temp < 0o C To increase population of ice crystals Seeding with Silver Iodide To increase population of water drops Stratiform Clouds Sodium Chloride or Urea
  15. 15. 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.
  16. 16. Ice crystal ProcessIce crystal Process  Bergeron processBergeron process of rain formation:of rain formation: A process that producesA process that produces precipitation; involves tiny iceprecipitation; involves tiny ice crystals in a supercooled cloudcrystals in a supercooled cloud growing larger at the expense of thegrowing larger at the expense of the surrounding liquid dropletssurrounding liquid droplets  Ice crystals and liquid cloud dropletsIce crystals and liquid cloud droplets must coexist in clouds at belowmust coexist in clouds at below freezingfreezing  AccretionAccretion or riming of ice crystals:or riming of ice crystals: Ice crystals grow larger by collidingIce crystals grow larger by colliding with the supercooled liquid droplets;with the supercooled liquid droplets; the droplets freeze into ice and stickthe droplets freeze into ice and stick to the ice crystalto the ice crystal
  17. 17. Mixed CloudsMixed Clouds
  18. 18. Seeding MaterialsSeeding Materials  The materials used in cloud seeding include two primaryThe materials used in cloud seeding include two primary categories, tied to the type of precipitation process involvedcategories, tied to the type of precipitation process involved » Glaciogenic (ice-forming)Glaciogenic (ice-forming) Silver iodide, dry ice andSilver iodide, dry ice and compressed liquid propanecompressed liquid propane  The second major category is focused on cloud systems whereThe second major category is focused on cloud systems where the warm (coalescence) process predominatesthe warm (coalescence) process predominates.. » Hygroscopic (water attracting)Hygroscopic (water attracting) materials such asmaterials such as salt, ureasalt, urea and ammonium nitrateand ammonium nitrate can be utilized. Of the hygroscopiccan be utilized. Of the hygroscopic materials, the most commonly used are salts.materials, the most commonly used are salts.
  19. 19. Silver IodideSilver Iodide  Why Silver Iodide ?Why Silver Iodide ? – It has a crystalline structure similar to ice crystal, and it acts as anIt has a crystalline structure similar to ice crystal, and it acts as an effective ice nucleus at temp. of -4effective ice nucleus at temp. of -4°C and lower°C and lower – Silver iodide, when burned, creates extra ice crystals in winterSilver iodide, when burned, creates extra ice crystals in winter clouds to increase snow fall. (The first AgI generator couldclouds to increase snow fall. (The first AgI generator could discharge 10discharge 101616 particles per gram)particles per gram) ((www.wmi.cban.com/www.wmi.cban.com/)) It can be distributed from the ground...It can be distributed from the ground...
  20. 20. Silver IodideSilver Iodide ……or from the air.or from the air.
  21. 21. Ground based Generator Automated High-Output Ground Seeding System Aircraft-mounted flaresCloud Seeding Aircraft
  22. 22. How Cloud Seeding WorksHow Cloud Seeding Works
  23. 23. How Cloud Seeding works?How Cloud Seeding works?  In cold cloud seedingIn cold cloud seeding.,.,  the introduction of an ice-forming nucleatingthe introduction of an ice-forming nucleating agent, (e.g., silver iodide) causes supercooledagent, (e.g., silver iodide) causes supercooled liquid water droplets to freeze. Once theseliquid water droplets to freeze. Once these droplets freeze, the initial ice embryos grow atdroplets freeze, the initial ice embryos grow at the expense of the water droplets around them.the expense of the water droplets around them. – The first freezing process is often referred to as aThe first freezing process is often referred to as a staticstatic seeding effectseeding effect, increasing the efficiency of the, increasing the efficiency of the precipitation process within the seeded cloud volume.precipitation process within the seeded cloud volume. – The second freezing process, resulting from release ofThe second freezing process, resulting from release of additional heat into the cloud, is often called theadditional heat into the cloud, is often called the dynamic effectdynamic effect, whereby the treated clouds are, whereby the treated clouds are invigorated, thus processing more moisture.invigorated, thus processing more moisture.
  24. 24. Warm Cloud Seeding at 2 to 3 km heights
  25. 25. Cold Cloud Seeding
  26. 26. A hole in a stratus cloud deck due to cloud seeding with aircraft, using dry ice This is where super cooled cloud droplets are converted into ice crystals , which then precipitate out of the cloud deck.
  27. 27. Indian ExperimentIndian Experiment  IITM, Pune was involved in cloud seedingIITM, Pune was involved in cloud seeding experiment for a period of 11 years in theexperiment for a period of 11 years in the seventiesseventies  Reported Increase in rainfall due to seedingReported Increase in rainfall due to seeding ~ 24%~ 24%  Different states have their own operationalDifferent states have their own operational programs whose success is still being debatedprograms whose success is still being debated
  28. 28. Interesting Applications Hail suppression Hurricane Modification Eg: Operation STORMFURY Fog Dispersion Defence Applications
  29. 29. Suppression of Hail  Cloud seeding canCloud seeding can be used to causebe used to cause rain instead of hail.rain instead of hail.  HoweverHowever suppressing hail insuppressing hail in one area oftenone area often causes more incauses more in another.another. ((twri.tamu.edu)
  30. 30. Thank You

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