Cyclones are centers of low atmospheric pressure, in which the air pressure increases from the centre to the outer areas.
Consequently winds flow from outside to the centres.
In cyclones winds blow in an anticlockwise direction in the northern hemisphere and in clock-wise in the southern hemisphere.
On the basis of their location and physical properties cyclones are of two types; temperate cyclones and tropical cyclones.
Here a description of only tropical cyclone is given.
The use of word ‘cyclone’ is implied for tropical cyclone here onwards.
Cyclone is a violent circular stormy, in which high velocity winds blow from outside to the centre and are associated with torrential rain.
Cyclones play an important role in the general circulation of the atmosphere.
A fully developed cyclone can transfer 3.5 billion tons of warm humid air within an hour.
In India, most of the cyclones occur in the post monsoon season, i.e. from October to December or in pre-monsoon season from April to May.
The life span of a cyclone is generally from 7 to 14 days.
The Movement of Cyclones–
The cyclone, with its whole system, moves forward from east to west (in Bay of Bengal) with a speed of 15 to 30 km per hour.
The cyclone that struck Orissa originated near Andaman & Nicobar Islands and reached Orissa on 29-10-1999, after many days.
Cyclones originate over the sea surface and dissipate as they reach land.
Where do the cyclones strike in India–
The eastern coast of India is the most cyclone affected region.
The cyclone prone states are; West Bengal, Orissa, Andhra Pradesh and Tamil Nadu:
Western coast is affected by the cyclones which originate in the Arabian Sea.
Gujarat on the west coast is most affected by cyclones.
The coastal areas and interior of Maharashtra are affected by cyclones too.
More cyclones originate in the Bay of Bengal and the Arabain Sea than any other seas of the world.
Devastation by cyclones
Trees are uprooted.
Lines of electricity and communication are destroyed.
Torrential rains cause floods.
High sea waves are generated in the sea by speedy cyclonic winds.
They strike the coastal areas like high wall of water and flood the areas upto 10-15 km from the coast.
In these areas houses, crops, roads, buildings, villages and cities one and all are submerged.
Landslides triggered by cyclonic rains are more devastating.
Developed countries have evolved measures to mitigate the fury of cyclones.
The warning of cyclone is issued.
On the contrary the people in developing countries get premature deaths.
In USA, a fierce hurricane named Hugho struck in September 1989.
Only 21 people lost their lives due to its impact, because a timely warming was issued, but contrary to this 1,39,000 people lost their lives in Bangladesh when a cyclone struck the country in 1991.