Severe cyclonic storm ‘Asani’, packing winds above 105 kmph and setting off heavy rain, is likely to make landfall on the eastern coast of India.

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) finalised the list.
• The WMO/ESCAP expanded to include five more countries in 2018 — Iran, Qatar, Saudi Arabia, United Arab Emirates and Yemen.

Why is it important to name cyclones?

• Adopting names for cyclones makes it easier for people to remember, as opposed to numbers and technical terms.
• It’s easier and less confusing to say “Cyclone Titli” than remember the storm’s number or its longitude and latitude.
• Apart from the general public, it also helps the scientific community, the media, disaster managers etc.
• With a name, it is also easy to identify individual cyclones, create awareness of its development, rapidly disseminate warnings to increase community preparedness etc.

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