Natural phenomena like the El Nino, La Nina, and the Indian Ocean Dipole, known as IOD, are some of the major factors in the variability of frequency and density of monsoon rainfall occurring every year in India. These climatic phenomena happen due to the temperature differences in the sea surface waters caused in the parts of the Indian Ocean.

UPSC students must be aware of the concepts and cycles of these phenomena as questions related to El Nino, La Nina, and the Indian Ocean Dipole are widely asked in the UPSC Prelims and Mains. At the Prelims level, the aspirants need to prepare well on the basics, functioning, and concepts of the Indian Ocean Dipole questions. For Mains, the aspirants should be more aware of these phenomena’ role in the Indian Monsoon.

In this article, we will discuss “what is Positive Indian Ocean Dipole and why has Positive IOD occurred a lot in recent past years in comparison to other phases of IOD.” We will also help you know the effects and impacts of Positive IOD and the effects caused in recent past years.

What is Indian Ocean Dipole?

Indian Ocean Dipole, by its name, is an atmospheric phenomenon that happens in the Indian Ocean. Also known as IOD, it causes temperature differences in the sea surface waters of the western regions around the Arabian Sea and eastern regions around the Bay of Bengal of the Indian Ocean. The Indian Ocean Dipole plays a significant role in deciding monsoon in the Indian Subcontinent. IOD is complemented mainly by El Nino and rarely by La Nina.

The Indian Ocean Dipole causes pressure differences due to the temperature differences in the parts of the Indian ocean. This leads to the flowing of westerly winds in the eastern and western regions of the Indian Ocean.

The cycle of IOD begins in April and May, which continues to go by October. It originates in the equatorial regions of the Indian Ocean. IOD can occur in three phases, neutral, negative, and positive. We will focus more on the Positive IOD and discuss its impacts on the Indian monsoon.

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What is the Positive Indian Ocean Dipole?

Positive Indian Ocean Dipole is one of the phases of Indian Ocean Dipole. The westerly winds get slower and weaker along the equator. This leads to warm water flowing to African regions. These temperature and wind changes in the Positive IOD also lead to an uprise in cool water from the Indian Ocean in the East.

This leads to temperature and pressure difference between the east and the west. The ocean water in the east of the Indian ocean gets cooler than usual, and the ocean water in the west gets warmer than usual. The Positive IODs are said to be good signs and aggregators of excessive rainfall in the monsoon.

The impacts of Positive Indian Ocean Dipole can have huge or minor aggravations to the El Nino, which can affect the Indian monsoon significantly when combined.

What are the Impacts of Positive Indian Ocean Dipole on Indian Monsoons?

The questions related to Indian Ocean Dipole and Indian Monsoon UPSC are majorly asked in the UPSC Mains. The Positive Indian Ocean Dipole seems to significantly affect Indian monsoons, especially when it comes to the Central and South regions of the Indian Subcontinent. 

The ENSO (El Nino Southern Oscillation) cycle shows a clear picture of how aggressive rainfalls occur in the Indian Subcontinent due to the Positive IODs complemented by El Nino.


  1. Positive IODs are the primary cause of increased rainfall during monsoon in the central regions of India.
  2. Positive IODs also negate the effects of ENSO, which can lead to even more aggressive monsoon rainfalls.
  3. Positive IODs are the potential reasons for cyclones in the Arabian Sea.
  4. Positive IODs cause SST variations along with below-normal rain in the eastern parts of India.
  5. Positive IODs lead westerly winds to cross the western ghats and go towards the southwest regions of India. Other winds cross the Himalayas and come downwards towards the central regions of India, causing Positive IODs to impact excessive monsoon rainfall in the Western and Southwest regions of India.
  6. The effects of IOD can also increase the impact of El-Nino-like anomalies and variations in the far-eastern regions of the Pacific. It can have higher interactions with the ENSO cycle and can amplify the effect of El-Nino.

Since 1980, there have been 12 Positive IODs and only one negative IOD in 2010, which was huge. Usually, it is seen that El Nino complements positive IODs, but in 2007, it was very rare to see that La Nina complemented positive IOD.

The consecutive happenings of Positive IODs from 1980 are considered a major concern as it was the primary reason for the Black Saturday Bushfires.

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Final Words

Natural phenomenons like El Nino, La Nina, and Indian Ocean Dipole (IOD) have significant effects on the Indian monsoon. From the above article, you have the Indian Ocean Dipole explained along with the effect of Positive IODs. The aggravation of Positive IOD with the El Nino can result in more excessive rainfalls in the Indian Subcontinent.

Positive IODs are the leading cause of aggressive rainfall, and Negative IODs are the cause of droughts. The topics and concepts related to natural phenomenons like Indian Ocean Dipole, El Nino, and La Nina are widely asked in the Prelims and Mains exams of the UPSC.

At UPSC Pathshala, we will help you sharpen and clear all your concepts with the extensive and interactive teaching our professional mentors have. We are a team of close to 200+ mentors who have only one goal in mind, “to help UPSC aspirants achieve their dreams”.Come join the holistic mode of UPSC preparation with UPSC Pathshala today!

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Positive Indian Ocean Dipole: Basics that Every UPSC Aspirant shouldn’t Miss
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Positive Indian Ocean Dipole: Basics that Every UPSC Aspirant shouldn’t Miss
What is Indian Ocean Dipole? What is Positive Indian Ocean Dipole? What are the impacts of Positive IODs on the Indian Monsoon? Read on to find out the answers to all these questions.
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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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