What explains the eastward flow of the equatorial counter-current?
[UPSC Civil Services Exam – 2015 Prelims]
(a) The Earth’s rotation on its axis
(b) Convergence of the two equatorial currents
(c) Difference in salinity of water
(d) Occurrence of the belt of calm near the equator
- Distinct surface wind patterns in the tropics drive the equatorial counter-currents.
- In most parts of the tropical Atlantic and Pacific Oceans, strong westward trade winds result in a westward surface flow.
- However, several hundred miles to the north of the equator, the winds weaken. This causes water to pile up where the winds are weak, resulting in a surface ocean that can be up to 6 inches (15 centimeters) higher and a thermocline up to 328 feet (100 meters) deeper than areas to the north.
- This excess water then flows eastward, leading to the formation of equatorial counter-currents.
- In the Indian Ocean, this current is situated several hundred miles south of the equator, while in all three oceans, it is concentrated above the thermocline in the upper 656 feet (200 meters).
- The intensity of the equatorial counter-current varies by season and month, with the Atlantic Ocean experiencing the strongest seasonal changes.
- The eastward flow in this ocean reaches its maximum during summer and fall, with speeds of up to 12 inches (30 centimeters) per second, disappearing in the spring.
- In contrast, the equatorial countercurrent in the Pacific Ocean exists year-round and is strongest during fall and winter, with slightly lower speeds.
Therefore, option (b) is the correct answer.