Question 37 from UPSC CSE 2015 - Geography

Question

What explains the eastward flow of the equatorial counter-current?

IASCODEX · Accepted Answer

Correct Option: D. Occurrence of the belt of calm near the equator

Strategy: Focus on why an eastward current exists counter to prevailing trade winds. The critical clue is the 'belt of calm' near the equator (the Doldrums), where winds are weak, allowing a pressure-gradient-driven eastward flow. Other options (Earth's rotation, convergence, salinity) either operate universally or don't directly create the eastward flow. The occurrence of the calm belt (option D) is thus the determining factor.

Key Info: The Equatorial Counter-Current is an eastward-flowing ocean current located just north of the equator in the Atlantic, Indian, and Pacific oceans. It flows between the North and South Equatorial Currents, moving from west to east.

This current forms because trade winds push water westward, causing it to accumulate along the western boundaries of ocean basins. This creates a surface slope with a higher sea level in the west. Water then naturally flows down this slope from west to east, forming the counter-current. This flow is strongest in the belt of calm known as the Doldrums, a zone near the equator (typically 5°N to 5°S) with weak or absent surface winds. The lack of wind in this zone reduces resistance and allows the pressure-gradient-driven current to develop.

Other factors are not the primary cause:
*   **Earth's rotation:** The Coriolis force mainly affects currents away from the equator and is not the driving force for the counter-current.
*   **Convergence of currents:** The meeting of the North and South Equatorial Currents primarily causes upwelling and vertical mixing, not an eastward flow.
*   **Salinity differences:** These influence large-scale thermohaline circulation, not the specific equatorial counter-current pattern.

Therefore, the equatorial counter-current arises chiefly from the horizontal pressure gradient, which is enabled by the calm zone near the equator.

IASCODEX · Answer

Option A: The Earth's rotation on its axis

IASCODEX · Answer

Option B: Convergence of the two equatorial currents

IASCODEX · Answer

Option C: Difference in salinity of water