UPSC Prelims 2015 · GS Paper I
Question 5: Geography
In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason?
AnswerUPSC’s answer is (b).
Tropical cyclones form over warm seas where air converges along the Inter-Tropical Convergence Zone, the low-pressure belt that supplies the initial disturbance. In the South Atlantic and the south-eastern Pacific the ITCZ lies north of the equator and seldom enters these southern tropical waters, so the triggering convergence is missing. Cold currents and strong wind shear add to the effect, but UPSC's decisive reason is the ITCZ.
Why each option is right or wrong
- (a) Cold currents cool these seas, but UPSC treats this as secondary to the missing convergence zone.
- (b) Correct: the ITCZ seldom occurs there, so cyclone-triggering convergence is absent.
- (c) The Coriolis force is adequate in these latitudes; it is weak only very near the equator.
- (d) Absence of land is no barrier: cyclones form over open oceans and need no land.
Worth knowing: Low sea surface temperature from cold currents is also widely cited for these regions, so options (a) and (b) can both be argued; UPSC's key is (b).
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper I, Series A. The paper on upsc.gov.in.