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Project Rain GaugeProject Rain Gauge (PRG) is a joint undertaking of Smart Communications, Inc. (SMART) and Manila ObservatorysKLIMA Climate Change Center, in cooperation with the Philippine Atmospheric, Geophysical and AstronomicalServices Administration (PAGASA) and the Department of Education.Project Rain Gauge aims to spark awareness in the study of earth science by building online meteorological dataprovided by a network of public high schools who monitor and record rainfall observations around the country. It alsoassists in disaster preparedness by providing a community-based early warning system for possible natural disasters

like landslides and flash floods.Importance of Rainfall MonitoringRainfall rate and quantity interact with many other factors to influence erosion, vegetative cover, groundwaterrecharge, stream water chemistry and runoff of nonpoint source pollution into streams.Rainfall observations from various sites are especially significant in the Philippines because of the country'smountainous terrains and islands. The Philippines is vulnerable to extreme rainfall events, i.e., droughts andexcessive rain. These events have had significants impacts on the different sectors of the society (e.g. agricultureand energy) and on society itself (e.g. when rainfall triggered landslides occur). Hence, it is critical to monitor rainfallamounts especially in the light of future climate change. Unfortunately, data from global models and the existinglimited number of ground stations do not capture the fine-scale rainfall patterns necessary to describe the localclimate. The addition of rain gauges in different parts of the country is valuable for rainfall monitoring.Project Rain Gauge endeavors to create a network of ground stations across the country via the Smart SchoolsProgram (SSP), SMARTs community service initiative for education, to provide supplementary data on local rainfallmeasurement in specific areas. Rainfall observations performed and recorded by the schools can be used for moreaccurate weather reporting and forecasting in local communities.

The first phase of Project Rain Gauge trained teachers from 17 SSP schools located in disaster-prone areas. Thepilot schools echo-trained other SSP partner schools near their respective divisions and added 33 more publicschools in the PRG network. Aside from the training, the new PRG member schools were also given manual raingauges.With proper nurturance of our countrys young minds, we will enjoy a scientific understanding of rain and bettermeans of responding to the changes in our environmental landscape.

Cloud seeding, a form of weather modification, is the attempt to change the amount or type

ofprecipitation that falls from clouds, by dispersing substances into the air that serve as cloud

condensation or ice nuclei, which alter the microphysical processes within the cloud. The usual intent is to

increase precipitation (rain or snow), but hail and fog suppression are also widely practiced in airports.

Terpenes are released by trees more actively during warmer weather, acting as a natural form of cloud

seeding. The clouds reflect sunlight, allowing the forest to regulate its temperature.

The most common chemicals used for cloud seeding include silver iodide and dry ice (frozen carbon

dioxide). The expansion of liquid propane into a gas has also been used and can produce ice crystals at

higher temperatures than silver iodide. The use ofhygroscopic materials, such as salt, is increasing in

popularity[citation needed]

because of some promising research results[citation needed]

.

Seeding of clouds requires that they contain supercooled liquid waterthat is, liquid water colder than

zero degrees Celsius. Introduction of a substance such as silver iodide, which has acrystalline structure

similar to that of ice, will induce freezingnucleation. Dry ice or propane expansion cools the air to such an

extent that ice crystals can nucleate spontaneously from the vaporphase. Unlike seeding with silver

iodide, this spontaneous nucleation does not require any existing droplets or particles because it

produces extremely high vapor supersaturations near the seeding substance. However, the existing

droplets are needed for the ice crystals to grow into large enough particles to precipitate out.

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In mid-latitude clouds, the usual seeding strategy has been predicated upon the fact that the

equilibrium vapor pressure is lower over ice than over water. When ice particles form in supercooled

clouds, this fact allows the ice particles to grow at the expense of liquid droplets. If there is sufficient

growth, the particles become heavy enough to fall as snow (or, if melting occurs, rain) from clouds that

otherwise would produce no precipitation. This process is known as "static" seeding.

Seeding of warm-season or tropical cumulonimbus (convective) clouds seeks to exploit the latent

heat released by freezing. This strategy of "dynamic" seeding assumes that the additional latent heat

adds buoyancy, strengthens updrafts, ensures more low-level convergence, and ultimately causes rapid

growth of properly selected clouds.

Cloud seeding chemicals may be dispersed by aircraft (as in the second figure) or by dispersion devices

located on the ground (generators, as in first figure, or canisters fired from anti-aircraft guns or rockets).

For release by aircraft, silver iodide flares are ignited and dispersed as an aircraft flies through the inflow

of a cloud. When released by devices on the ground, the fine particles are carried downwind and upwards

by air currents after release.

An electronic mechanism was tested in 2010, when infrared laser pulses were directed to the air

above Berlin by researchers from theUniversity of Geneva.[1]

The experimenters posited that the pulses

would encourage atmospheric sulfur dioxide and nitrogen dioxide to form particles that would then act as

seeds.[1]

How is artificial rain produced?

R.Narasimhan, Chennai

ANSWER 1: The need to develop and improve rain-making techniques in terms of design, operation,

monitoring and evaluation by giving them a more scientific character is today's need.

This includes using computers to study cloud formations and help the rain-making operations achieve the

goals of the project. The role of weather modification, or rain-making, is an important component in water

resource management.

The process involved in artificial rain-making involves three easy-to-understand stages. The first stage is

agitation. That is using chemicals to stimulate the air mass upwind of the target area to rise and form rain

clouds.

The chemicals used during this stage are calcium chloride calcium carbide, calcium oxide, a compound of

salt and urea, or a compound of urea and ammonium nitrate. These compounds are capable of absorbing

water vapour from the air mass, thus stimulating the condensation process.

The second stage is called building-up stage. Here the cloud mass is built up using chemicals such as kitchen

salt, the T.1 formula, urea, ammonium nitrate, dry ice, and occasionally also calcium chloride to increase

nuclei which also increase the density of the clouds. In the third stage of bombardment chemicals such as

super-cool agents: silver iodide and dry ice are used to reach the most unbalanced status which builds up

large beads of water (Nuclei) and makes them fall down as raindrops.

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In planning every stage a high degree of expertise and experience is required, in selecting the types and

amounts of chemicals to be used, while taking into consideration weather conditions, topographical

conditions, wind direction and velocity as well as the location or delimitation of the area for chemical

seeding. Several other ideas are also involved in rain making. Rockets containing rain-making chemicals can

be fired into the clouds either from the ground or from aircraft.

A jet of rain-making chemicals is shot from a highly pressurised cannister directly into the cloud base, so asto coerce clouds which normally hang above mountain tops to cluster up and rain on the mountain or their

slopes.

Rain-making chemicals are added to super-cooled clouds, i.e., those at altitudes above 18,000 metres, to

stimulate the formation of ice crystals in the cloud or cloud cluster.

The Hindu S&T desk

* * *

ANSWER 2: Artificial rain is produced by spraying clouds with substances like Silver Iodide (costly) or

cheaper ones like solid carbon dioxide (dry ice) or even finely powdered Sodium Chloride. The process is

called seeding.

Often there are clouds, but no rain. This is because of a phenomenon called supercooling. The temperature

of the cloud might be close to zero and there might even be crystals of ice in it.

The water vapour in the cloud does not condense to liquid water. The super cooling gets disturbed by

spraying the cloud with the chemicals mentioned above, using a small aeroplane for the purpose.

The `super' phenomena (cooling, heating, saturation etc.) are perverse in a sense. Very pure water when

heated in a clean vessel, often does not start boiling when expected. Crystals of the photographer's hypo

(Sodium thiosulphate) easily dissolve in a little water when heated. But on cooling, crystals do not separate

out.

If the vessel is shaken vigorously, or if a small crystal of hypo is freshly added, then crystallization starts

immediately.

Making artificial rain is a similar way of intervening in the super cooling phenomenon.