More Tropical cyclones occur in the Bay of Bengal than the Arabian Sea and the ratio is approximately 4:1. An analysis of the frequency of cyclones on the east and west coasts of India between 1891 and 1990 shows that nearly 262 cyclones occurred on the east coast and 33 cyclones occurred on the west coast during this period.
Tropical cyclones are one of the nature’s most violent manifestations and potentially the deadliest of all meteorological phenomena. It is a unique combination of violent wind, heavy rainfall, mountainous waves in sea.
Tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air.
There are several conditions which are favorable for the formation of a tropical cyclone;
- Tropical cyclones develop in the vicinity of inter tropical convergence zone (ITCZ) or near equatorial trough where relative cyclonic vorticity is already present as a quasi steady feature. This zone is found nearly 5° north or south of the equator.
- Tropical cyclones develop in maritime air mass over sea areas where sea surface temperature > 26.5°C and overlying tropical atmosphere is convectively unstable.
- Formation of a well-marked low pressure area or depression close to ITCZ / near equatorial trough which later on develops into a full fledged tropical cyclone is favored by the arrival of the low pressure wave from the east
- It is found that over the regions which are climatologically favorable for the development of tropical cyclones, the vertical shear/winds is weak. The cyclones generally do not form when the shear of the zonal flow between 950 and 200 hPa exceeds 10 m /s.
- There should be enough moisture up to the mid atmospheric level.
- There should be pre existing vortex in the low level of the atmosphere whichwill support in the formation of tropical cyclones.
- There should be conditional instability of second kind (CISK) present in the atmosphere.
Why TropicaL Cyclones are more common in Bay of Bengal/east coast of India?
1.On the eastern coast, the shape of the land around the Bay of Bengal ensures that the winds are slower and weaker over the ocean.
2.This part of the Indian Ocean is also fed by a constant source of freshwater from giant rivers such as the Ganga and the Brahmaputra.This water that empties into the Bay of Bengal takes up the space of the evaporated top layers, warming up at the surface and rising up as moisture. This makes it difficult for the warm layers of water to mix properly with the cooler layers of water below, keeping the surface always warm and ready to feed any potential cyclone over it.
3.Furthermore, the Bay of Bengal also welcomes cyclones formed over the Pacific. As there is no landmass big enough to stop these Pacific cyclones, they pass through Malaysia and the Gulf of Thailand and enter the Bay of Bengal
4.Surface sea temperatures and humidity are directly related to the formation of cyclones. Since, the Bay of Bengal receives high average rainfall, the possibility of cyclone formation is also high.
5.The winds over the Bay of Bengal are said to be a lot more sluggish compared to the Arabian Sea and therefore, the winds fail to reduce the surface temperature of the sea.
6.The average temperature in the Bay of Bengal around the year is high – about 28 degrees. Warm air-currents intensify this. When the bay receives fresh water from the Brahmaputra and other rivers, the surface temperature is replenished, resulting in t…
Why less frequent in Arabian Sea?
- Dry air intrusion: Dry winds blow from West to East, bringing air devoid of moisture from the Arabian Peninsula (desert region). Dry air (without water vapour) will literally choke tropical cyclones.
- Strong wind shear: The monsoon trough causes strong wind shear in the region, which hampers cyclone development.
- Most cyclones formed along the western coast of the country veer towards Oman — 58 per cent of the storms that form in the Bay of Bengal (BOB) hit the coast while only 25 per cent of those in the Arabian Sea does.The country’s western coast is helped by mountains in East Africa that tend to direct a lot of wind towards the Arabian Peninsula, dissipating heat much more efficiently throughout the Arabian Sea