Cyclones and Anticyclones

Cyclones

A cyclone represents a low pressure system in the lower atmosphere where the winds tends to converge towards a common centre. It is developed when a low pressure area is created surrounded by a high pressure area. In such a system the winds blow towards the centre and due to the Coriolis effect they start blowing in a circular manner. In the northern hemisphere cyclonic winds blow in the anti-clockwise direction and in the Southern hemisphere they blow in the clockwise direction. On the basis of regions of their occurrence the cyclones are called tropical and temperate cyclones.

The tropical cyclones generally develop due to local heating resulting in a very low pressure. They develop mostly over the seas in the summer months or during the period of rapid seasonal change. Bay of Bengal witnesses a number of tropical cyclones during the southwest monsoon season and also during the retreating monsoon season. They move in the direction of the prevailing winds and cause a lot of damage in the coastal areas. These cyclones are associated with high velocity winds and heavy rainfall and accompanying floods. The cyclones of the temperate regions develop due to convergence of the cold and warm air masses and they move eastwards in the belt of the westerly winds. They are most intense over the continents in winter. Some of these cyclones affect Indian weather conditions in the northern parts of the country where they cause rainfall and snowfall in winter season. Here they are called the westerly disturbances.

The tropical cyclones are smaller in size but more intense than the temperate cyclones. The central part of the tropical cyclone is an area of calm conditions and it is called the eye of the cyclone. The temperate cyclones do not have such central calm areas.

Cyclones and cyclonic storms are known by various names in different parts of the world. They are called cyclones or depressions in the Bay of Bengal, hurricanes in West Indies, Typhoons in China Sea, Willy-willies in Australia and tornadoes in the North America.

Anticyclones

An anticyclone is a high pressure centre surrounded by low pressure all around. Due to the high pressure in the centre the winds are divergent and radiate from the high pressure centre. In the northern hemisphere they circulate in the clockwise direction while in the southern hemisphere their direction is anti-clockwise. The weather associated with anticyclones is clear skies without rain. The most important anticyclonic areas are the subtropical high pressure belts and the polar high pressure belts.

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