In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not orig

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UPSC Prelims is a competitive examination conducted in India. This question is from the 2015 UPSC Prelims Geography paper.

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Question

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

Accepted Answer

Correct Answer: A — Sea surface temperatures are lowStep-by-step Solution:Tropical cyclones (also called hurricanes or typhoons in different regions) require very specific conditions to form and intensify. The most critical are: (1) sea surface temperature (SST) above 27°C; (2) Coriolis force (so the system develops rotation — absent within 5° of equator); (3) low vertical wind shear; (4) pre-existing low-pressure disturbance; (5) upper-level divergence.In the South Atlantic Ocean and the South-Eastern Pacific Ocean, cyclones are extremely rare or absent for the following primary reasons:Sea surface temperatures remain cooler than the 27°C threshold — even in the southern summer (December-February). Cold ocean currents — particularly the Benguela Current (upwelling cold water along the west African/South Atlantic coast) and the Humboldt/Peru Current (cold water along the South American Pacific coast) — keep SSTs suppressed below cyclone-generation thresholds. Without sufficiently warm water to provide energy through evaporation and latent heat release, tropical cyclone genesis is impossible.Additionally, high vertical wind shear across both these basins throughout the year inhibits the organised convective development needed for cyclone formation. Extremely rare exceptions (like Cyclone Catarina in 2004 in the South Atlantic) confirm the rule rather than contradict it.Why other options are incorrect:Option B (ITCZ seldom occurs): The ITCZ does affect these regions, but its absence alone is not the primary explanation. The ITCZ provides a triggering mechanism, but the fundamental barrier is cold SSTs which prevent tropical cyclone intensification regardless of convergence zones.Option C (Coriolis force too weak): The Coriolis force is indeed weak at the equator and absent at the equator itself — but the tropical latitudes (5°-30° poleward) in these basins do have sufficient Coriolis force for cyclone rotation. The problem is not Coriolis force — it is SST.Option D (Absence of land): Tropical cyclones form over open oceans — land inhibits them. The absence of land in these regions would, if anything, theoretically favour cyclone formation. This option is therefore incorrect.Key Concept: Tropical cyclone formation requirements: SST >27°C; Coriolis force (>5° from equator); low wind shear; pre-existing low pressure; warm, moist air in lower troposphere; upper-level outflow. Cold ocean currents suppressing SST: Benguela Current (South Atlantic) — upwelling; Humboldt/Peru Current (SE Pacific) — upwelling. Warm ocean currents favouring cyclones: Gulf Stream (North Atlantic); Kuroshio (North Pacific); warm Indian Ocean waters. Cyclone-prone basins: North-West Pacific (most active), North Atlantic, North Indian Ocean, South Indian Ocean, North-East Pacific.

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

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

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