Tropical Cyclones Diagram, Image Credit: www.rayburntours.com
Cyclones developed in the regions lying between the tropics of Capricorn and Cancer are called Tropical Cyclones which are not regular and uniform like extra tropical or temperate cyclones. There are numerous forms of these cyclones, which vary considerably in shape, size, velocity and weather conditions. The weather conditions of low latitudes mainly rainfall regimes are largely controlled by Tropical Cyclones.
1. Size of tropical cyclones varies considerably. On an average their diameters range between 80 km and 300 km.
2. Weak cyclones move at the speed of about 32 km per hour while hurricanes attain the velocity of 180 km per hour or more.
3. Tropical cyclones become more vigorous over the oceans but become weak and feeble while moving over land areas. This is why these cyclones affect only the coastal areas e.g. Tamil Nadu, Orissa and West Bengal coasts of India.
4. The centre of the cyclone is characterized by extremely low pressure. Tropical cyclones are not characterized by temperature variations in their different parts because they do not have different fronts.
5. There are no different rainfall cells hence each part of the cyclones yields rainfall. Tropical cyclones are not always mobile. Normally, they move from east to west under the influence of trade winds.
6. There is a specific time of year during which tropical cyclones are more likely to form (summer season).
Types of Tropical Cyclones
Generally they are divided into 4 major types:
1. Tropical disturbances
2. Tropical depressions
3. Tropical storms
4. Hurricanes or typhoons
Origin of Tropical Cyclones
On an average, tropical cyclones are formed due to development of low pressure of thermal origin (Tropical cyclones diagram:1)
. They develop when the following requirements are fulfilled:
1. There should be continuous supply of abundant warm and moist air. Tropical cyclones originate over warm oceans having surface temperature of 27°C.
2. Higher value of Coriolis force is required for the origin of these cyclones.
3. They are associated with inter-tropical convergence (lTC), which extends from 50-300N latitudes during summer season.
4. There should be anti-cyclonic circulation at the height of 9000 to 15000 m above the surface disturbance.
There are 6 major regions of the tropical cyclones e.g. (1) West Indies, Gulf of Mexico, and Caribbean Sea. (2) Western North Pacific Ocean including Philippines, Islands, China Sea, and Japanese Islands. (3) Arabian Sea and Bay of Bengal. (4) Eastern Pacific coastal region off Mexico and Central America. (5) South Indian Ocean of Madagascar (Malagasi), and (6) Western South Pacific Ocean, in the region of Samoa and Fiji Island and the east and north coasts of Australia.
Tropical cyclones are very severe disastrous natural hazards which inflict heavy loss to human lives and property in terms of destruction of buildings, transport systems, water and power supply systems, disruption of communication system, destruction of standing agricultural crops, domestic and wild animals, natural vegetation, private and public institutions etc. Through damages caused by high velocity winds, floods and storm surges.