Topics related to natural phenomenons like El Nino, La Nina, and the Indian Ocean Dipole questions are asked in the UPSC Prelims and Mains exams. These weather conditions and mechanisms were lately seen causing effects in the major regions of Australia, South America, and South Asia. It was asked most often in the GS paper of the UPSC exams.

Taking these topics into significance, we will discuss in the article below, “what is the Indian Ocean Dipole? its characteristics, and what are the effects it causes on monsoon seasons?”

What is Indian Ocean Dipole?

Indian Ocean Dipole (IOD) is something that happens in the Indian Ocean. It is an atmospheric-ocean-based phenomenon just like the El Nino and La Nina, where the temperatures of the sea surface waters get warmed up in the positive phase of IOD and get cooled up in the negative phase of IOD.

The Indian Ocean Dipole, also known as Indian Nino, is actually the difference between the Arabian Sea that is the western part of the Indian Ocean, and the Bay of Bengal, the eastern part of the Indian Ocean. The Indian monsoon widely depends upon these phenomenons like the IOD, El Nino, and La Nina.

Indian Ocean Dipole Characteristics

How IOD Develops?

IOD develops due to various atmospheric phenomena, which leads to changes in water surface temperature. It develops in April and May, which peaks up till October and originates in the equatorial parts of the Indian Ocean.

How Temperature Differences Occurs?

The temperature and wind changes in the Positive IOD lead to an uprise in cool water from the Indian Ocean in the East. The temperature difference is caused between the western and eastern parts of the Indian Ocean, which creates pressure difference and ultimately resulting in the flowing of warm and cold winds in the eastern and westerns regions of the Indian Ocean.

What are the Three Phases developed in IOD?

IOD develops three phases, including a Positive phase, a Negative phase, and a Neutral Phase.

Phases of the Indian Ocean Dipole

Positive Indian Ocean Dipole

This phase of the Indian Ocean Dipole is very favourable and beneficial for higher monsoons in the Indian regions. The positive IOD occurs due to the westerly winds getting weaker alongside the equator. This makes the warm water flow towards the African regions.

This change in the wind also results in cool water rising from the deep ocean in the east. This also leads to a rise in warmer than normal water around the west of the Indian ocean and cooler than normal water in the east of the tropical Indian ocean.

Negative Indian Ocean Dipole

This phase of the Indian Ocean Dipole is the opposite and obstructs the progressions and occurrences of monsoon in the Indian regions. The negative IOD occurs due to the westerly winds getting strong and amplified alongside the equator. This here leads to more passage of warmer water to the Australian regions.

This intensification in wind results in cooler than normal water in the western regions of the Indian Ocean and warmer than normal water in the eastern regions of the tropical Indian ocean.

Neutral Indian Ocean Dipole

In this phase of Indian Ocean Dipole, the water flows from the Pacific in the South of the Indonesian islands to the northwest regions of Australia, keeping the sea waters warm. The westerly winds blow alongside the equator, and the air above this whole area rises and falls across the western halves of the Indian Ocean basin.

How Does Indian Ocean Dipole El Nino Impact on Monsoon?

Natural climatic phenomenons like El Nino, La Nina, and IDC can have various effects in the modes of excessive rainfall or intensive droughts. Below are some of the impacts of these phenomenons on the Indian Subcontinent –

  1. The monsoon was uneven for several recent years in the Indian Subcontinent. The ENSO cycle was able to show effective graphs relating to the droughts that were caused due to IOD and El Nino.
  2. The studies state that the year when positive IOD hits are when excessive rainfall is seen in the central parts of India.
  3. A positive IOD can also completely negate the effects of ENSO (El Nino Southern Oscillation), which can result in amplified monsoon with excessive rainfall, as happened in the years 1983, 1994, and 1997.
  4. Positive IOD can also give rise to more cyclones in the Arabian sea region.
  5. Negative IODs can accumulate and combine with the effects of El Nino to give rise to severe droughts caused in the Indian Subcontinent.

Here are Some More

  1. Negative IODs can also give rise to tropical cyclones in the regions of the Bay of Bengal. During this, it also causes Cyclogenesis in the Arabian Sea to get suppressed.
  2. The two poles of the IOD that are the Western Pole around the African Coast and the Eastern Pole around Indonesia, were cumulatively and independently affecting the rainfall quantity of the monsoons happening in the Indian Subcontinent every year.
  3. The connections of IOD were mostly resulting in below-normal rains and SST in the eastern Indian ocean and more than normal rain in the central regions of India.
  4. The westerly winds coming from the western parts of the Indian Ocean (Arabian Sea) get blocked by western ghats and makes them cause rains in the southwest regions of India. The other winds that flow from the west get blocked by the Himalayas and lead to more rain in India’s northern and central regions.

Recent Phenomenons Caused by Indian Ocean Dipole 

In the year 1997 and 1998, the effects of IOD were significantly seen that resulted in major monsoons in the Indian Subcontinent. This occurred due to a major positive IOD. The same also occurred in the year 2006.

There have been close to 12 positive IODs since the year 1980 till now and just one huge negative IOD in 2010. The consecutive occurrences of positive IODs are rare and considered a major concern as this also resulted in the Black Saturday bushfires.

In 2007, a very rare phenomenon happened, where a positive IOD accumulated together with La Nina. This was historical as the only time it occurred before was in 1967 (as per the historical records after discovery).

A powerful negative IOD that was accumulated and complemented by a strong La Nina resulted in major 2010-2011 floods in Queensland and Victorian floods in 2011.

Now, as per forecasting and modelling, it is said that these trails of consecutive positive IODs are projected to occur at least twice for every 1000 years. It is also seen that positive IODs increase by strength, frequency, and quantity of occurrence in the 20th century.

What are the Effects of Indian Ocean Dipole on El Nino?

Indian Ocean Dipole El Nino can have inductive effects of SST variations and anomalies being caused. The Indian Ocean Dipole (IOD) can cause and amplify various El Nino-like variations and anomalies, causing SST to be more powerful in the far-eastern regions of the Pacific. IOD can have major interactions with the ENSO cycle and amplify the rate of effects of El Nino.

What was the 2020 IOD Positive Cycle?

The 2019 East Africa cyclones killed thousands due to warmer than normal waters offshore. It started with Cyclone Idai and continued with the 2019-20 cyclone season of the South-western Indian Ocean.

The Australian bushfires and droughts were caused due to a convective IOD cycle that brought warmer and dry air downwards to the continent of Australia.

Also, the 2020 Jakarta floods were caused due to a convective IOD cycle that prevented moist air near tropical regions and went to southwest Asia instead of going to Australia.


The above article might have got you useful insights and must have got you Indian Ocean Dipole explained. Indian Ocean Dipole, along with El Nino and La Nina, is one of the major factors. We face different frequencies of rainfall, droughts, and overall monsoon every year. These phenomenons that cause temperature differences in the sea surface waters lead to the emergence of different kinds of winds which ultimately flow to various regions of Asia, Australia, and South America.

The positive IODs are the main reason for excessive rainfall, whereas negative IODs lead to droughts and cyclones. The IOD can have amplified or weaker effects on the Indian monsoon, depending upon the cumulations with El Nino and very rarely La Nina.

The topics related to El Nino, La Nina, Indian Ocean Dipole, and Indian Monsoon UPSC are widely asked in the UPSC Prelims and Mains. As a UPSC aspirant, you should be thorough with the basics and functioning of these phenomena and the updates on the recent occurrences of these phenomena.

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What is Indian Ocean Dipole? Important Details about IOD for UPSC Aspirants
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What is Indian Ocean Dipole? Important Details about IOD for UPSC Aspirants
Find out What is Indian Ocean Dipole? What are the effects of Positive, Negative, and Neutral IODs on the Indian Monsoons and important concepts regarding IOD for UPSC preparation.
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Shilpa is a professional web content writer and is in deep love with travelling. She completed her mass communication degree and is now dedicatedly playing with words to guide her readers to get the best for themselves. Developing educational content for UPSC, IELTS aspirants from breakthrough research work is her forte. Strongly driven by her zodiac sign Sagittarius, Shilpa loves to live her life on her own notes and completely agrees with the idea of ‘live and let live. Apart from writing and travelling, most of the time she can be seen in the avatar of 'hooman' mom to her pets and street dogs or else you can also catch her wearing the toque blanche and creating magic in the kitchen on weekends.

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