UPSC Prelims 2015 Q5: Geography – Atmosphere & Climatology
In the South Atlantic and South - Eastern Pacific regions in tropical latitudes, cyclone does not
originate. What is the reason?
- (a) Sea surface temperatures are low
- (b) Inter - Tropical Convergence Zone seldom occurs
- (c) Coriolis force is too weak
- (d) Absence of land in those regions
Answer: (b) Inter - Tropical Convergence Zone seldom occurs
Explanation
Why no cyclones in the South Atlantic and South-Eastern Pacific?
Tropical cyclones need a starting disturbance.
That usually forms along the Inter-Tropical Convergence Zone (ITCZ).
In these two regions the ITCZ seldom moves south of the Equator.
| Option | Verdict | Reason |
|---|---|---|
| (a) Sea surface temperatures are low | Partly true | Cold Benguela and Peru currents cool these seas; but this is not the official key |
| (b) Inter-Tropical Convergence Zone seldom occurs | Correct (official key) | No convergence, so no seed disturbance |
| (c) Coriolis force is too weak | Incorrect | It is weak only within about 5 degrees of the Equator, in every ocean |
| (d) Absence of land in those regions | Incorrect | Cyclones form over open sea |
Conditions for a tropical cyclone:
| Condition | Detail |
|---|---|
| Warm sea | Above 27 degrees Celsius |
| Coriolis force | Enough to spin the system |
| Low wind shear | Lets the storm grow upward |
| A prior disturbance | Usually on the ITCZ |
Answer: (b) Inter-Tropical Convergence Zone seldom occurs.
Why each option is right or wrong
- (a) Incorrect. Low sea surface temperatures do play a part, but the official key is (b).
- (b) CORRECT. The Inter-Tropical Convergence Zone seldom occurs over these regions.
- (c) Incorrect. The Coriolis force is weak only very near the Equator, in all oceans alike.
- (d) Incorrect. Absence of land does not stop cyclones; they are born over the sea.
Key point
No cyclones in the South Atlantic and South-Eastern Pacific: the ITCZ seldom reaches there, and cold currents (Benguela, Peru) keep the sea cool.
Remember
South Atlantic: no ITCZ, cold currents, no cyclones.
Common mistakes
- Choosing Coriolis force, which applies only close to the Equator.
- Thinking cyclones need land to form; they weaken over land.
- Marking low sea temperature alone; UPSC's key is the ITCZ reason.
Exam tip
Cyclone needs four things: warm sea, Coriolis force, low wind shear and an ITCZ disturbance.
Sources
- NCERT Class XI — Fundamentals of Physical Geography, Ch 10 (Atmospheric Circulation and Weather Systems)
- India Meteorological Department — Frequently Asked Questions on Tropical Cyclones