From UPSC perspective, the following things are important :
Prelims level : Cyclone Mandous
Mains level : Tropical Cyclones
Cyclone Mandous crossed the north Tamil Nadu coast with fierce winds and heavy downpour.
- ‘Mandous’ was a name submitted by WMO member United Arab Emirates and is pronounced as ‘Man-Dous.’
- It means ‘treasure box’ in Arabic.
What are Tropical Cyclones?
- A tropical cyclone is an intense circular storm that originates over warm tropical oceans and is characterized by low atmospheric pressure, high winds, and heavy rain.
- Cyclones are formed over slightly warm ocean waters. The temperature of the top layer of the sea, up to a depth of about 60 meters, need to be at least 28°C to support the formation of a cyclone.
- This explains why the April-May and October-December periods are conducive for cyclones.
- Then, the low level of air above the waters needs to have an ‘anticlockwise’ rotation (in the northern hemisphere; clockwise in the southern hemisphere).
- During these periods, there is an ITCZ in the Bay of Bengal whose southern boundary experiences winds from west to east, while the northern boundary has winds flowing east to west.
- Once formed, cyclones in this area usually move northwest. As it travels over the sea, the cyclone gathers more moist air from the warm sea which adds to its heft.
Requirements for a Cyclone to form
There are six main requirements for tropical cyclogenesis:
- Sufficiently warm sea surface temperatures
- Atmospheric instability
- High humidity in the lower to middle levels of the troposphere
- Enough Coriolis force to develop a low-pressure centre
- A pre-existing low-level focus or disturbance
- Low vertical wind shear
How are the cyclones named?
- In 2000, a group of nations called WMO/ESCAP (World Meteorological Organisation/United Nations Economic and Social Commission for Asia and the Pacific) decided to name cyclones.
- It comprised Bangladesh, India, the Maldives, Myanmar, Oman, Pakistan, Sri Lanka and Thailand, decided to start naming cyclones in the region.
- After each country sent in suggestions, the WMO/ESCAP Panel on Tropical Cyclones (PTC) finalized the list.
- The WMO/ESCAP expanded to include five more countries in 2018 — Iran, Qatar, Saudi Arabia, United Arab Emirates and Yemen.
- The atmospheric disturbances which involve a closed circulation of air around a low pressure at the center and high pressure at the periphery, rotating anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere (due to the Coriolis force) are called “cyclones”.
Cyclones are broadly classified into two types based on the latitudes of their origin-
- Tropical cyclones
- Temperate/Extra-tropical cyclones
- Tropical cyclones develop in the region between the tropics of Capricorn and Cancer. These are violent storms that originate over oceans in tropical areas and move on to the coastal regions bringing large-scale destruction caused by violent winds, very heavy rainfall and storm surges. These cyclones are one of the most devastating natural calamities.
- Tropical cyclones mostly move along with the direction of trade winds, so they travel from east to west and make landfall on the eastern coasts of the continents.
- Tropical cyclones are known by different names depending on the regions of the world. They are known as Hurricanes in the Atlantic, Typhoons in the Western Pacific and South China Sea, Willy-willies in Western Australia and Cyclones in the Indian Ocean.
Temperate Cyclones/Extra-Tropical Cyclones
- It occurs between 30°-60° latitude in both hemispheres (in between the Tropic of Cancer and the Arctic circle in the northern hemisphere and in between the Tropic of Capricorn and the Antarctic Circle in the southern hemisphere).
- These cyclones move with the westerlies and are therefore oriented from west to east.
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