Tropical Cyclones

Tropical Cyclones Tropical cyclones, the most de­structive of nature's phenomena, are known to form over all tropical oceans, except South Atlantic and the South Pacific, during certain seasons. These cyclones have a thermal origin. They are believed to form in the Inter­Tropical Convergence Zone. (ITCZ), a narrow belt at the equator, where the trade winds of the northern and southern hemispheres meet.

ITCZ is a 'legion of high radiation energy which supplies the necessary heat Jor the vaporisation of sea water into the air. This moist unstable air rises, generates convective clouds and leads to an atmospheric disturbance with a fall in surface atmospheric pressure. This causes a convergence of surrounding air towards this region of low pressure.

The converging mass of air gains a rotary motion because of what is known as the Coriolis force caused by the rotation of the earth. However, under favourable circumstances, such as high sea-surface temperatures, this low pressure area can get accentuated. The convective instability builds up into an organised system with high speed winds circulating around the low pressure interior. The net result is a well-formed cyclone.

The ideal conditions for the development of tropical cyclones are-(i) quiet air, (ii) high temperature, (iii) highly saturated atmospheric conditions.
Tropical cyclones never originate over land, although they often penetrate far into the margins of continents. But they soon lose their strength after crossing the coast and penetrating inland.