Previous Year Question
With reference to ‘Indian Ocean Dipole (IOD)’ sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct?
1 only
2 only
Both 1 and 2
Neither 1 nor 2
Correct Answer: B
Detailed Solution
Statement 1—Incorrect
The Indian Ocean Dipole is an ocean-atmosphere phenomenon associated with the Indian Ocean.
It is determined by the difference in sea-surface temperature between the tropical western Indian Ocean and the eastern Indian Ocean near Indonesia.
The statement substitutes the eastern Indian Ocean with the eastern Pacific Ocean. The eastern Pacific is associated with the El Niño-Southern Oscillation, not with the eastern pole of the IOD.
Phases of the IOD
Positive IOD:
The western Indian Ocean becomes warmer than normal, while the eastern Indian Ocean becomes cooler than normal.
Convection and rainfall may increase over the western part, while rainfall around Indonesia may decline.
A positive IOD can sometimes support the Indian monsoon.
Negative IOD:
The eastern Indian Ocean becomes relatively warmer and the western Indian Ocean relatively cooler.
Convection increases around Indonesia, while Indian monsoon conditions may be adversely affected.
Statement 2—Correct
El Niño is generally associated with a weakened Indian monsoon and reduced rainfall.
However, the influence of El Niño on the monsoon is not identical in every year.
If a positive IOD develops along with El Niño, favourable thermal and atmospheric conditions over the Indian Ocean can partly counteract the adverse impact of El Niño.
Thus, the IOD can modify or influence El Niño’s impact on the monsoon.
This does not mean that every positive IOD will completely cancel an El Niño; the outcome depends on the timing and strength of both phenomena.