Q. 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. IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
2. An IOD phenomenon can influence an El Nino's impact on the monsoon.

Select the correct answer using the code given below: (UPSC Prelims 2017)
Answer: 2 only
Notes: The correct answer is [B] 2 only. Often called the "Indian Niño," the Indian Ocean Dipole (IOD) is a major driver of climate variability in the Indian Ocean region.Detailed Analysis

• Location of Temperature Difference (Statement 1 – Incorrect):The IOD is defined by the difference in sea surface temperatures between two poles within the Indian Ocean itself:
  1. The Western Indian Ocean (near the Arabian Sea/East Africa).
  2. The Eastern Indian Ocean (near Indonesia/South of Sumatra).The statement incorrectly mentions the Eastern Pacific Ocean, which is actually the domain of the El Niño-Southern Oscillation (ENSO). The IOD is strictly an Indian Ocean phenomenon.
• Influence on El Niño (Statement 2 – Correct):The IOD and El Niño can interact in significant ways. While El Niño generally has a negative impact on the Indian monsoon (often causing droughts), a Positive IOD can counteract this effect. A strong Positive IOD brings more moisture and rainfall to India, effectively "canceling out" or mitigating the drying effect of El Niño. Conversely, a Negative IOD can worsen a weak monsoon.

Understanding the Phases of IODThe "Dipole" refers to the see-saw of temperatures between the west and east:

Phase	Western Indian Ocean	Eastern Indian Ocean	Impact on Indian Monsoon
Positive IOD	Warmer than normal	Cooler than normal	Beneficial: Leads to above-normal rainfall and can offset El Niño.
Negative IOD	Cooler than normal	Warmer than normal	Harmful: Suppresses monsoon rainfall and can lead to droughts.

Key Relationship: IOD vs. ENSOWhile they are independent phenomena, they often occur simultaneously. For instance, the record-breaking drought and wildfires in Australia in 2019–2020 were driven by one of the strongest Positive IOD events in history, which caused extreme cooling and dry air over the eastern part of the ocean.