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| Tuesday, 16 March 2004 |
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The First Inter Monsoon Season of Sri Lanka normally prevails from mid-March to mid- May. During this Season, we will experience a number of weather conditions, some times extremes. Wind and temperature conditions in this season enhance the development of convective clouds called cumulonimbus. This could produces lightning, tornado and hailstorms, which are equally hazardous when a well-developed cumulonimbus clouds generate them, said W.K. Abeysinghe, Deputy Director Meteorology yesterday. He said convection becomes considerable in April with the sun rising overhead over many parts of Sri Lanka and' peak and vigorous development of convective clouds does occur normally after second week of April. But under certain conditions intense convection is possible even before April particularly in Inter monsoons preceded by dry and warm Northeast monsoons. The lower part of a cumulonimbus cloud consists mostly of water particles and drops but the region above about the five kilometers consists mainly of super-cooled water drops and ice Since rain starts with the falling ice particles from these upper parts of the cloud, we sometimes may experience rain with ice (Hailstorms). But fortunately we are living in a ironical country where the low level temperatures are very much above the freezing temperature of water. For this reason, unlike in colder parts of the world, the ice tends to melt before reaching the earth. As a result hazards caused by hailstorms are not severe in our country. But we may experience thundershowers with ice balls of about 1-2 centimetres in size during the inter monsoon. Vigorous convection leads to development of small-scale cyclone type systems called Tornado, Tornadoes average about 100 meters across. Their destructive power is caused both by their tremendous winds, which may exceed 200kt (400 kmph), and by the great radial gradient of pressure, which causes explosive destruction of buildings etc in their path. Their durations is very variable, about 10 to 15 min on average. Since the understanding of a tornado in our country is very little, the destruction caused even by mild tornadoes seem to have been interpreted by the public and documented by the media as those of a cyclone or a storm. |
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