UPSC Prelims 2015 GS Paper I · Q5 of 100 Geography medium

In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason?

  1. (a) Sea surface temperatures are low
  2. (b) Inter-Tropical Convergence Zone seldom occurs ✓ UPSC's answer
  3. (c) Coriolis force is too weak
  4. (d) Absence of land in those regions

Why the answer is (b)

• Tropical cyclones form where the Inter-Tropical Convergence Zone provides low-level convergence and rising air over warm seas.

• In the South Atlantic and south-eastern Pacific, cool currents (Benguela, Humboldt) keep sea temperatures below 26–27 °C and the ITCZ stays north of the equator, seldom moving into these regions; strong vertical wind shear adds to the suppression — option (b) per the official key.

• Coriolis force (c) is adequate away from the equator; absence of land (d) is irrelevant since cyclones form over sea.

• Hence option (b).

Why the other options are wrong

(a) Sea surface temperatures are low
Low SST contributes, but the key identifies the absent ITCZ as the reason.
(c) Coriolis force is too weak
Coriolis force is sufficient at those latitudes.
(d) Absence of land in those regions
Cyclones form over sea; land absence is irrelevant.

Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2015, held on 23 August 2015. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

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