UPSC Mains 2014 GS Paper 1 Q19: model answer
Tropical cyclones are largely confined to South China Sea, Bay of Bengal and Gulf of Mexico. Why?
What the question wants
Explain why tropical cyclones are concentrated in the South China Sea, Bay of Bengal and Gulf of Mexico.
How to structure it
Why?: the conditions for cyclones and why these seas meet them.
- Conditions
- Each region
- Note on other regions
How to think it through
A cyclone needs a warm bath, a spin and a quiet sky above. These three seas offer all three. Remember the question's 'largely': cyclones also form elsewhere.
Model answer
In the North Indian Ocean the Bay of Bengal sees about four times as many cyclones as the Arabian Sea, according to IMD records.
Conditions for a tropical cyclone
- Sea surface temperature above 26.5°C over a large area, to about 50 m depth.
- Coriolis force strong enough to spin the air, so formation is between about 5° and 20° latitude, not at the equator.
- Low vertical wind shear, so the warm core is not torn apart.
- A pre-existing low-pressure disturbance and high humidity in the mid-troposphere.
Why these three seas
- South China Sea and West Pacific: the world's largest warm pool, easterly waves and the ITCZ; typhoons hit the Philippines, China and Vietnam.
- Bay of Bengal: shallow, warm and semi-enclosed; low salinity from river inflow keeps the surface warm; remnants of Pacific storms enter across Myanmar; the funnel-shaped coast also intensifies surges.
- Gulf of Mexico and Caribbean: warm Gulf waters and easterly waves from Africa feed Atlantic hurricanes.
A caveat
Cyclones also form in the Arabian Sea, South Indian Ocean (Madagascar, Australia) and the eastern Pacific. Warming is making the Arabian Sea more active.
Draw: World map with cyclone zones and local names: hurricane, typhoon, cyclone.
Keywords, cases and data to drop in
26.5°C SST, Coriolis, wind shear, warm pool, easterly waves, ITCZ.
Where most answers lose marks
- Missing the 'why' for each region and listing only the general conditions.
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Question text as printed in the official UPSC Civil Services (Main) question paper. The model answer is original Battle IAS work; use it to learn structure, not to memorise.
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