Cyclones are centres 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 anti-clockwise direction in the northern hemisphere and in clockwise 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.
When do cyclones occur?
Cyclone is a phenomenon. It is concentrated to certain seasonal cyclic segment.
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. The movement of cyclone in a direction is like the movement of a spinning top.
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 Arabian Sea than any other seas of the world.
Devastation by cyclones
The violent winds of a cyclone destroy whatever come in their –
- from thatched cottage to the palaces, forts built of concrete, iron and stones.
- trees are uprooted;
- lines of electricity and communication are destroyed;
- torrential rains cause floods; floods wreak havoc all around;
- 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. They are broadcasted and telecasted at right time. This saves the life of people.
- 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.
On the contrary the people in developing countries get premature deaths.
- 1,39,000 people lost their lives in Bangladesh when a cyclone struck the country in 1991.
Some DOs and DON’Ts before, during and after the cyclone
- Listen to the radio for advance information and advice.
- Keep considerable margin of time for safety.
- A cyclone may change direction, speed, or intensity within a few hours, so stay tuned to the radio for updated information.
If high velocity winds or severe gales are forecasted for your area –
- Store or secure loose boards, corrugated iron sheets, old tin boxes, anything else that could become dangerous.
- Close the windows tightly to prevent them from breakage.
- Move to the safe shelter built for this purpose, or leave the area on the advice of some authoritative government agency.
When the storm strikes –
- Stay in the house and take shelter in the stronger portion of your house.
- Listen to the radio and follow instructions.
- Open windows of the safe portion of the house if the roof begins to lift.
- Find shelter if you are in open at the hitting time of the cyclone.
- Do not go out of your house or to a beach during or lay down along an elevated footpath in open field the storm. Cyclone often generates large surges in these oceans or lakes.
Cyclone is violent circular storm. In its centre the air pressure is extremely low. High velocity winds flow towards the centre.
Bibliography : NIOS Geography Book