DO WE NEED ARTIFICIAL RAIN IN MARCH?
According to media news during last few weeks, a team of Thai experts have arrived recently to launch a cloud seeding program to produce artificial rain in Sri Lanka. News bulletins also have informed us that the practical part of the project will take place in March 2019.
Most of Sri Lankans, including school children and teachers, may have felt wonder to hear of producing artificial rain in March because the first Inter Monsoon season in our country establishes in mid-March every year. Another important fact is, as a result of very heavy rain falls fell in the latter part of second Inter Monsoon season and beginning of North east Monsoon last year, almost all the catchment reservoirs are still half full. It is a known fact that convective rains in first Inter Monsoon (FIM), March-April, bring a significant amount of precipitation in many areas of the country.
As we learn in the school, one part of the water cycle is the precipitation of water drops to ground from clouds. Whole process of rain consists of a series of physical changes within the lower atmosphere. Moist air rises up, becomes saturated with moisture due to cooling in atmospheric levels above about 500 meters, saturated moisture condenses to form water droplets, combine tiny droplets forming large water drops and ultimately fall down as rain complete the process. This natural process is supported and accelerated by a number of atmospheric parameters when requirements are naturally fulfilled.
Then…..what is the meaning of artificial rain making?.
With the development of scientific and technological applications, man could observe all atmospheric parameters and physical processes even at very high atmospheric levels and a number of experiments were launched with the hope of accelerating some steps in producing rain artificially by using chemicals and some materials. If we peep into a brief history, in 1946, Vonnegut in the U.S.A. found that particles of silver iodide, acting as ice nuclei, were capable of forming ice crystals out of water droplets at a temperature of 4 degrees Celsius below zero. In the same year Vincent Schaefer, also in the U.S.A. discovered that dry ice (solid carbon dioxide), which exists 70 degrees Celsius below zero, when crushed and scattered in a cloud of super-cooled water droplets, produces ice particles which multiply very rapidly in numbers. Field experiments conducted by Langnluir and Schaefer showed that these techniques were reasonably successful in producing some degree of precipitation from ordinarily non-precipitating cumulus clouds. Several techniques have been used in the 'seeding' of ice clouds. For instance, fine particles of silver iodide or dry ice have been scattered from air-craft flying at cloud base, the reason being that the updrafts in the clouds tend to carry the seeding particles upwards and hence prolonging their life-time. In other experiments solutions of silver iodide and acetone have been burned by ground-based burners and the smoke allowed to rise into selected clouds.
For further details, you can scan the web sites to search for ’cloud seeding’ or ‘’artificial rain making’’.
A number of countries launch cloud seeding processes to produce rain in instances with severe scarcity of rain for long periods leading to drought. As the clouds develop only in high humid atmosphere and they tend to move with prevailing wind streams, upper air observations are performed before performing cloud seeding to verify whether the conditions are favourable for seeding clouds. Otherwise seeding cloud is a pretty expensive practical. It may be a successful attempt for countries with significantly large geographical area but not for tiny land masses.
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