Wednesday, 02 April 2014 10:52




The word 'cyclone' comes from the Greek word 'cyclos', meaning 'coiling of a snake'. It was coined by Heary Piddington who worked as a rapporteur in Kolkata during the British Raj. Tropical cyclones over the Atlantic are called hurricanes; those over the Pacific are called typhoons.

What is a tropical cyclone?

A tropical cyclone is a storm system characterized by a low-pressure centre, which produces strong winds and flooding rain. A tropical cyclone feeds on heat released by the condensation of moist air. The latent heat gets converted into kinetic energy and feeds the strong winds emerging out of it. Cyclonic storms have counterclockwise rotation in the Northern Hemisphere and clockwise in the Southern Hemisphere. Developed over warm water bodies — ocean and seas — they lose their strength once they move over land. They also help in the global atmospheric circulation mechanism by carrying heat and energy away from tropics towards temperate latitudes.

Tropical cyclone has a central cloud-free region of calm winds, known as the “eye” of the cyclone, with a diameter varying from 10 to 50 km. Surrounding the eye is the “wall cloud region” characterised by very strong winds and torrential rain, which is about 10-150 km wide. Winds over this region rotate around the centre and resemble the “coils of a snake”. Wind speed falls off gradually away from this core region. The height of the cyclone is about 15 km. A mature cyclone releases energy equivalent to that of 100 hydrogen bombs.

What are the different types of tropical cyclones?

Tropical cyclones are formed in eight basins — Northern Atlantic, Northeastern Pacific, North Central Pacific, Northwestern Pacific, Northern Indian Ocean, Southwestern Indian Ocean, South and Southwestern Pacific and Southeastern Indian Ocean. Each basin has a different naming system. In the North Atlantic Ocean, Northwest Pacific Ocean east of the International Date Line and South Pacific Ocean, they are called hurricanes. Typhoon is the name given to a tropical cyclone formed in the Northwest Pacific Ocean west of the dateline. In the southwest Pacific Ocean and southeast Indian Ocean, it’s called a severe tropical cyclone. Similarly, tropical cyclones in the north Indian Ocean and southwest Indian Ocean are called severe cyclonic storm and tropical cyclone respectively.

What is the process of naming cyclones?

The regional body responsible for monitoring a tropical cyclone in a particular basin makes a list of cyclone names for the particular basin. There are five such bodies which keep 10 pre-designated lists of cyclone names. The names are proposed by the member countries. For instance, the names of cyclones in the northern Indian Ocean are contributed by Bangladesh, India, Maldives, Myanmar, Oman, Pakistan, Sri Lanka and Thailand.


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Last Updated on Wednesday, 02 April 2014 11:53