The Indian Ocean Dipole (IOD), also known as the ‘Indian Nino’, has gained significant attention due to its potential impact on weather phenomena, including the El Nino and the Indian Monsoon. Operating over a relatively small area of the Indian Ocean, the IOD’s behaviour influences atmospheric and oceanic conditions that steer the path of monsoons.
Navigating the Intricacies of IOD
The IOD behaves in a manner similar to the El Nino phenomenon but is confined within the Indian Ocean, between the Indonesian and Malaysian coastline in the east, and the African coastline near Somalia in the west. The IOD can exist in a positive state when the western part of the Indian Ocean, near the Somalia coast, gets warmer than the eastern part. On the other hand, it is termed negative when the western part of the Indian Ocean is cooler.
Mechanisms and Impact of Negative and Positive IOD Events
In a negative IOD event, the air circulation in the Indian Ocean basin moves from west to east – from the African coast towards the Indonesian islands – pushing surface waters from west to east. This causes the air to rise and helps the prevailing air circulation. When this circulation becomes stronger, it results in the Indonesian region becoming warmer than usual, leading to hotter rising air. Under such circumstances, the system reinforces itself, resulting in a negative IOD condition.
In the case of a positive IOD event, the prevailing air circulation weakens and can sometimes reverse direction. As a result, the African coast warms up, while the Indonesian coastline cools down. Positive IODs often develop during an El Nino event, while negative IODs are associated with La Nina. The impact of IOD on rainfall varies significantly based on whether the IOD is positive or negative.
IOD: Past Events and Consequences
The IOD has been instrumental in influencing rainfall patterns globally. For instance, in 2019, a strong IOD event developed during the late monsoon season, compensating for the deficit rainfall during June (30% deficiency). This deficit was initially attributed to a developing El Nino, which eventually did not transpire.
El Nino Southern Oscillation (ENSO): An Inter-relationship
El Nino and La Nina are part of the El Nino Southern Oscillation (ENSO) phenomenon, affecting global weather events. During an El Nino, the eastern side of the Pacific Ocean warms up due to weaker wind systems, resulting in lesser displacement of warm waters. On the contrary, during La Nina, the opposite happens. In India, El Nino usually suppresses monsoon rainfall, implying a complex interplay between ENSO and the Indian Monsoon.
Importance of IOD and ENSO for Prelims and Mains
Given their significant impact on global weather and the Indian Monsoon, understanding the dynamics of IOD and ENSO is crucial. For instance, the UPSC Civil Services Examination in 2017 included a reference to the IOD in the context of forecasting the Indian Monsoon. Recognising the intricate relationship between the IOD and El Nino can thus help in successful preparation for such competitive examinations.
While these climatic phenomena exhibit predictable behaviours, their interactions and impacts have potential implications for major weather events across the world. As changes in these phenomena’s strength and frequency potentially impact the Indian monsoon’s behaviour, examining these elements becomes crucial in the light of climate change and its associated risks.