INDIAN OCEAN DIPOLE 

1. Context 

• The forthcoming monsoon season in India faces the likelihood of being influenced by the EI Nino phenomenon.
• However, there are hopes that a positive Indian Ocean Dipole (IOD) event could counterbalance the effects of El Nino.
• The IOD, a weaker ocean-atmosphere interaction similar to El Nino, occurs in the Indian Ocean and has the potential to mitigate the impacts of El Nino to some extent.

2. Current Status

• While El Nino has already established itself in the Pacific Ocean this year, the IOD is currently in a neutral phase. 
• The latest update from Australia's Bureau of Meteorology reveals that all international climate models suggest a possible development of a positive IOD event in the coming months.
• Additionally, the India Meteorological Department (IMD) bulletin states an 80 per cent probability of a positive IOD occurring during the June-August 2023 season.

3. Understanding El Nino and IOD

• El Nino, known as the Indian Nino, refers to a phenomenon where the eastern side of the Pacific Ocean becomes warmer due to weakened wind systems.
• Conversely, during La Nina, the opposite occurs.
• These conditions, collectively referred to as El Nino Southern Oscillation (ENSO), impact weather patterns globally and suppress monsoon rainfall over India.
• Similarly, the IOD, sometimes called the Indian Nino, occurs in the Indian Ocean between the Indonesian and Malaysian coastline in the east and the African coastline near Somalia in the west.
• It is characterized by one side of the equatorial ocean becoming warmer than the other.
• A positive IOD occurs when the western side near the Somalia coast becomes warmer, while a negative IOD indicates cooler temperatures in the Western Indian Ocean.

4. Relationship between ENSO and IOD

• IOD events often coincide with El Nino with a positive IOD typically developing during El Nino periods.
• Conversely, a negative IOD is sometimes associated with La Nina. While studies suggest that ENSO can trigger IOD events, there is evidence that IOD events can occur independently, driven by local circulations or subsurface processes within the equatorial Indian Ocean.
• Interestingly, strong IOD and ENSO events can influence each other's circulation patterns.

5. Impacts of IOD

• A positive IOD event brings increased rainfall along the African coastline and the Indian subcontinent while suppressing rainfall over Indonesia, Southeast Asia and Australia.
• Conversely, during a negative IOD event, the impacts are reversed.
• However, it is important to note that the impacts of IOD events are generally weaker compared to ENSO events.

Image source: Climate.gov

6. Hope for positive IOD

• Given the expected development of a strong El Nino in the Pacific Ocean this year, the possibility of a positive IOD event provides hope for balancing its effects.
• The case of the 2019 late monsoon season serves as an example, where a strong IOD Compensated for the initial deficit rainfall attributed to a developing El Nino.

7. The Way Forward

• As the monsoon season approaches, the possibility of a positive IOD event offers optimism for mitigating the impact of El Nino on rainfall patterns.
• Monitoring the development of the IOD and considering updated forecasts will be crucial in understanding its potential effects.
• While the IOD's impacts are relatively weaker than ENSO, there remains a glimmer of hope for a positive outcome this year.