RAS question
The Indian Ocean Dipole (IOD) affects Indian monsoon when:
Correct answer: (A) Positive IOD strengthens monsoon (warmer western Indian Ocean).
A positive Indian Ocean Dipole strengthens the Indian monsoon when the western Indian Ocean is warmer and the eastern Indian Ocean is cooler.
Explanation
A positive IOD means warmer conditions over the western Indian Ocean and cooler conditions towards the eastern side. This pattern is linked to stronger moisture supply and a stronger Indian monsoon. The verified MAUSAM article records strong positive tropical Indian Ocean dipole events with a significant increase in seasonal summer monsoon rainfall over India, and notes that positive Indian Ocean dipole events may reduce the influence of an El Nino event on the Indian monsoon. That is why option A is the best answer. The key exam point is not that El Nino is irrelevant, but that the Indian Ocean's own east-west temperature contrast can modify monsoon strength and sometimes offset El Nino's negative effect.
Why the other options are wrong
- (B) El Nino matters, but it is not the only control because the IOD is also a significant Indian Ocean driver of monsoon behaviour.
- (C) IOD cannot be treated as having no effect, since a positive IOD is linked here with stronger moisture supply and stronger monsoon conditions.
- (D) A negative IOD does not strengthen the monsoon in this framing; the positive phase strengthens it, while the negative phase weakens it.
Concept
This tests Indian monsoon teleconnections, especially how Indian Ocean sea-surface temperature anomalies interact with ENSO. It recurs in RAS because monsoon variability is central to Indian climatology, agriculture, drought and disaster questions.