Cyclone Hazard And Its Management

The term“cyclone” introduced by British meteorologist Henry Piddington (1797–1858) in 1848, perhaps < Greek kyklôn revolving (presentparticiple of kykloûn to revolve, verbal derivative of kýklos; seecycle); apparently confused by Piddington with kýklōma wheel, snake’s coil.

An atmospheric system characterized by the rapid inward circulation of air masses about a low-pressure center, usually accompanied by stormy, often destructive weather. Cyclones circulate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. A violent tropical storm, especially one originating in the southwestern Pacific Ocean or Indian Ocean.

An atmospheric circulation system in which the sense of rotation of the wind about the local vertical is the same as that of the Earth's rotation. Thus, a cyclone rotates clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. In meteorology the term cyclone is reserved for circulation systems with horizontal dimensions of hundreds (tropical cyclones) or thousands (extratropical cyclones) of kilometers. For such systems the Coriolis force due to the Earth's rotation, which is directed to the right of the flow in the Northern Hemisphere, and the pressure gradient force, which is directed toward low pressure, are in opposite directions. Thus, there must be a pressure minimum at the center of the cyclone, and cyclones are sometimes simply called lows.

A severe weather system with low central pressure. In the fully matured stage, it develops an eye at the center where there is no weather. The eye is surrounded by an inner circle of intense winds and rotating cloud mass. Around the inner circle is the outer circle, which has less fierce weather. The diameter of a cyclone can extend up to 320 miles (500 km). These are known as cyclones if they form in the Bay of Bengal and the Arabian Sea, where the wind speed is between 34 and 64 knots. The same name applies to the storms in the South Pacific region but when the speed exceeds 65 knots. All cyclones are given names by the World Meteorological Organization (WMO).