What explains the eastward flow of the equatorial counter-current?
- (a) The Earth's rotation on its axis
- (b) Convergence of the two equatorial currents ✓ UPSC's answer
- (c) Difference in salinity of water
- (d) Occurrence of the belt of calm near the equator
Why the answer is (b)
• The North and South Equatorial Currents, driven west by the trade winds, pile up water on the western side of ocean basins.
• Between them, in the doldrums where winds are weak, this accumulated water flows back eastward as the Equatorial Counter-Current, driven by the pressure gradient created by the convergence of the two currents — option (b).
• The Earth's rotation (a) deflects currents but does not cause the counter-flow; salinity (c) is not the driver; the calm belt (d) permits but does not explain it.
• Hence option (b).
Why the other options are wrong
- (a) The Earth's rotation on its axis
- Rotation deflects currents; it does not create the counter-current.
- (c) Difference in salinity of water
- Salinity differences do not drive the counter-current.
- (d) Occurrence of the belt of calm near the equator
- The calm belt allows the flow but is not its cause.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2015, held on 23 August 2015. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.