What is the Indian Ocean Dipole (IOD)?
The Indian Ocean Dipole (IOD) is a naturally occurring climate phenomena affecting both the ocean and atmosphere. The IOD is characterised by the oscillation of sea surface temperatures in the Indian Ocean. The IOD affects the weather pattern globally, particularly in regions near the Indian Ocean, including parts of Southeast Asia, Eastern Africa and Australia.
The IOD has two phases – a “positive” phase and a “negative” phase.
During the “positive” phase of the IOD, low-level winds blow from east to west, along the equator.
These wind changes cause warm water to be pushed to the western part of the Indian Ocean. As the warm water moves west, cold deep waters are brought up to the surface in the eastern part of the Indian Ocean.
As such, the western Indian Ocean becomes warmer and wetter, leading to more rain in places like Eastern Africa. Meanwhile, the eastern Indian Ocean becomes cooler and drier, causing less rain in areas like Southeast Asia and Australia.
This pattern is reversed during the “negative” phase of the IOD, where the eastern Indian Ocean becomes warmer and wetter, leading to more rain in places like Southeast Asia and Australia. The western Indian Ocean becomes cooler and drier, resulting in less rain in Eastern Africa.
These phases emerge on a year-to-year basis. The maximum intensity of the IOD occurs during boreal fall season (September to November).
In addition to rainfall patterns, air quality in Southeast Asia and the number of tropical cyclones in the Asian region can be altered due to the IOD.
Are the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) the same?
Both the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) are climate processes that have alternating warm and cool phases and occurs on a year-to-year basis. But they are distinct processes which operate independently. The IOD occurs in the Indian Ocean while the El Niño Southern Oscillation occurs in the Pacific Ocean.
The two processes can interact with one another. Changes in the condition in one ocean can alter wind patterns and atmospheric pressure, which can then influence conditions in the other ocean.
What happens when the phases of the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) occur at the same time?
Sometimes, the Indian Ocean Dipole (IOD) can occur together with the El Niño Southern Oscillation (ENSO). When the IOD and ENSO phases occur at the same time, they can significantly influence global weather patterns.
Typically, the “positive” phase of IOD occurs with the El Niño phase of ENSO, enhancing dry conditions in Asia and Australia. Correspondingly, the La Niña phase of ENSO tends to coincide with the “negative” IOD phase, bringing wetter conditions to Asia and Australia.
Interactions between the IOD and ENSO often bring about extreme weather conditions to the Southeast Asian region and surroundings. For example, in 2006, the “positive” phase of IOD occurred with El Niño which resulted in numerous extreme weather events, as depicted in the graphic below.
The simultaneous occurrence of the IOD and ENSO will recur. Early detection of and preparation for the associated extreme weather conditions can help mitigate their impacts on lives and livelihoods of millions living in the Southeast Asian region.