Previous Year Question
In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason?
Correct Answer: A
Detailed Solution
Tropical-cyclone formation generally requires:
Sea-surface temperature of approximately 26.5°C or higher.
Warm water extending to sufficient depth to maintain evaporation and latent-heat supply.
Adequate atmospheric moisture and instability.
Relatively weak vertical wind shear.
Sufficient distance from the equator for the Coriolis force to initiate rotation.
A pre-existing low-pressure disturbance.
South-Eastern Pacific Ocean:
The cold Humboldt or Peru Current and coastal upwelling along the western coast of South America keep surface waters comparatively cold.
The ocean therefore cannot provide sufficient heat and water vapour to sustain tropical-cyclone formation.
South Atlantic Ocean:
The cold Benguela Current and coastal upwelling along south-western Africa reduce sea-surface temperatures.
Vertical wind shear is also frequently strong, which inhibits the organisation of cyclonic circulation.
Other options:
Option (b): The limited presence of the ITCZ may be a contributing condition, but low sea-surface temperature is the principal and direct reason represented by the options.
Option (c): Coriolis force is weak very close to the equator, but the entire tropical South Atlantic and South-Eastern Pacific regions do not lie within that narrow equatorial belt.
Option (d): Tropical cyclones originate over oceans; absence of land does not inhibit their formation.