Context
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
