UPSC Prelims 2015 · Question 14 of 98
UPSC Prelims 2015 question on Equatorial Counter Current
- ExamUPSC CSE
- Year2015
- PaperGeneral Studies Paper I
- SubjectGeography
- TopicOceanography
- DifficultyHard
- TypeDirect
What explains the eastward flow of the equatorial counter-current?
Show answer
Answer: D. Occurrence of the belt of calm near the equator
Verdict
The answer is the occurrence of the belt of calm near the equator. The equatorial counter current flows eastward because the doldrums provide a zone of light winds.
Analysis
The trade winds drive surface water westward, but the land masses along the western boundaries block that flow, so sea level piles up in the west and an eastward horizontal pressure gradient develops. In the doldrums, the belt of calm near the equator, winds are too light to oppose that gradient, so water flows back eastward down the slope, against the prevailing wind direction. The rotation of the Earth explains the general deflection of currents but not this specific reversal. Convergence of the two equatorial currents describes an effect rather than a cause, and salinity differences drive deep thermohaline circulation, not this surface current.
Source
Encyclopaedia material on the equatorial counter current.
How to crack it
Distinguish the enabling condition from the driving force. The pressure gradient is the driver, but the question asks what explains the current, and the current exists only where the wind is too weak to suppress it. When a phenomenon is described as counter to the prevailing force, look for the option describing the absence of that force rather than the presence of another.