The Indian Ocean Dipole (IOD) ( or Indian Nino) is defined as the difference in sea surface temperature between the western pole of the Arabian Sea (western Indian Ocean) and an eastern pole south of Indonesia which has an impact on the climate of Australia and other nations in the Indian Ocean Basin. Indian Ocean Dipole is a major contributor to rainfall variability in the surrounding Indian Oceanic region. Indian Ocean Dipole is an important part of the Geography Syllabus of the UPSC Civil Services Examination which is being explained in this article.

Indian Ocean Dipole - Concept

• As the name says, the Indian Ocean dipole occurs in the Indian Ocean, and the word dipole denotes two opposing properties: poles of the same material.
• Indian Ocean Dipole is linked to the Indian Oceanic sides with opposite temperature characteristics.
• The Indian Ocean Dipole (IOD), also known as the Indian Nino, is a periodic oscillation of sea surface temperatures in which the western Indian Ocean becomes warmer (positive phase) and then colder (negative phase) than the eastern Indian Ocean.
• This irregular shift of temperature in the Indian Ocean is called Indian Ocean Dipole.
• It is similar to El Nino and La Nina in the Pacific Ocean.

Mechanism

• The Indian Ocean is bounded on three sides by landmasses, it is the warmest of the five oceans on the planet.
• Water from the Pacific flows into the Indonesian Ocean from the islands of Indonesia and Australia on the eastern side, influenced by tropical easterlies.
• Tropical Easterlies, which are found between 0 and 30 degrees latitude, travel from the northern hemisphere's northeastern side to the southern hemisphere's southeastern side.
• The chilly arctic waters do not mingle with the water of the Indian Ocean since it is landlocked from the north by the Eurasian Landmass.
• The temperature of the Indian Ocean fluctuates as water from the Pacific Ocean combines with water from the Indian Ocean.
• The many phases of IOD are determined by variations in the Indian Ocean. The surface water temperature is as follows:
  1. Neutral Indian Ocean Dipole (IOD)
  2. Positive Indian Ocean Dipole (IOD)
  3. Negative Indian Ocean Dipole (IOD)

Neutral IOD

The IOD's neutral phase begins in the spring when the sun's rays are evenly dispersed throughout the northern and southern hemispheres.

• Easterlies flow between 0-30 degrees North and 0-30 degrees South of the equator as a result of this.
• The surface temperature of oceanic waters is affected by these Easterlies/ Trade winds.
• When warm water from the Pacific Ocean interacts with water from the Indian Ocean, the temperature is evenly distributed in both the eastern and western Indian Oceans.
• The Neutral Period of the Indian Ocean Dipole (IOD) is the name given to this phase.

Positive Indian Ocean Dipole(IOD)

• During the positive IOD Phase, more warm water from the Pacific Ocean begins to migrate towards the Indian Ocean, pushed by strong Trade Winds/ Easterlies.
• The African continent locks the Indian Ocean on its western side, this warm water accumulates on the western side of the ocean due to the impact of trade winds.
• On the eastern edge of the Indian Ocean, due to thermocline as the surface warm water is withdrawn, deep underground chilly water begins to upwell.

• This forms a warm water dipole on the western side of the Indian Ocean, resulting in low pressure on that side of the ocean.

• In addition, the cold water on the eastern side of the Indian Ocean causes a high-pressure area in this region of the ocean.
• In a Low-pressure area, Warm air condenses, and clouds form due to evaporation and convection.
• Warmer sea surface temperatures in the western Indian Ocean compared to the east, easterly wind anomalies over the Indian Ocean, and reduced cloudiness in Australia's northwest, resulting in less rainfall in southern Australia and other South-Eastern countries.

Negative Indian Ocean Dipole(IOD)

• During the negative IOD Phase, Westerlies become more prominent than the easterlies. Which pushes the Warm water from the western side of the Indian Ocean towards the Eastern side.
• As a result, warm water accumulates on the western side of the Indian Ocean, and Coldwater upwells on the Western side due to the transfer of surface water in the Eastern Direction
• Thich causes a dipole, with warmer temperatures on the eastern side of the

• The Indian Ocean and cooler temperatures on the western side.
• As a result, the western half of the Indian Ocean has a High-Pressure zone, while the eastern side experiences a Lower Pressure zone.
• Condensation and precipitation occur in the North West Australian region and South East Asian countries due to low pressure in the Eastern Indian Ocean.
• Drought-like conditions exist along the western African continent's coast, with detrimental consequences.
• India by lesser rainfall in this region.

Impact of Indian Ocean Dipole on Indian Monsoon

• Studies have indicated that a positive IOD year brings more rain to central India than usual.
• In various ENSO years, such as 1983, 1994, and 1997, it was shown that a positive IOD index typically offsets the effect of ENSO, resulting in higher Monsoon rainfall.
• Furthermore, it was discovered that the IOD's two poles – the eastern pole (near Indonesia) and the western pole (off the African coast) – had independent and cumulative effects on the amount of rain that fell on the Indian subcontinent during the Monsoon.
• There is a link between below-normal SST in the eastern Indian Ocean and above-normal rain in central India, as well as vice versa.
• A negative IOD, on the other hand, works in tandem with El Nino to cause severe drought.
• At the same time, Positive IOD causes more cyclones in the Arabian Sea than typical.
• In the Bay of Bengal, negative IOD causes stronger cyclogenesis (the formation of tropical cyclones) than typical. During this time, cyclogenesis in the Arabian Sea is reduced.
• However, there is an oddity in the IOD and Monsoon phenomenon.

Impact of Indian Ocean Dipole on El-Nino

• Dipoles in the Indian Ocean El Nino can have an inductive influence on SST fluctuations and anomalies.
• The Indian Ocean Dipole (IOD) can generate and exacerbate numerous El Nino-like fluctuations and anomalies, leading SST to be stronger in the Pacific's far east.
• IOD can have significant interactions with the ENSO cycle, amplifying the pace of El Nino's impacts.

Impact of Indian Ocean Dipole on Australia

• The impact of a delayed monsoon may have ramifications for Australian summer crops, resulting in a 28 percent decrease in planted area in 2019–20.
• A positive IOD is typically associated with below-average winter-spring rainfall in southern and central Australia, as well as a more severe fire season in South-East Australia.
• The El-Nino Southern Oscillation (ENSO) in the tropical Pacific Ocean remains neutral.
• When ENSO is neutral, it has minimal effect on Australian and world climate, implying that other factors are more likely to take precedence.

Recent Phenomenons Caused by Indian Ocean Dipole

• The impacts of IOD were strong in 1997 and 1998, resulting in heavy monsoons in the Indian Subcontinent.
• This occurred as a result of a significant positive IOD. In 2006, the same thing happened.
• Since 1980, there have been around 12 positive IODs and only one significant negative IOD in 2010.
• Consecutive incidences of positive IODs are uncommon and cause serious worry since they contributed to the Black Saturday bushfires.
• An extremely unusual occurrence occurred in 2007 when a positive IOD was built with La Nina.
• This was significant since it had only happened once previously, in 1967. (as per the historical records after discovery).
• A severe negative IOD that accumulated and was augmented by a strong La Nina led to catastrophic floods in Queensland in 2010-2011 and Victorian floods in 2011.
• According to forecasting and modeling, these trails of successive positive IODs are expected to occur at least twice every 1000 years.
• Positive IODs are also shown to grow in strength, frequency, and amount of occurrence throughout the twentieth century.

Conclusion

One of the key contributors, along with El Nino and La Nina, is the Indian Ocean Dipole. Every year, we see varying levels of rainfall, drought, and general monsoon. These phenomena that create temperature variations in sea surface waters result in the formation of numerous types of winds, which eventually move to diverse parts of Asia, Australia, and South America. Positive IODs are mostly responsible for excessive rainfall, whereas negative IODs cause droughts and cyclones. Depending on the combination of El Nino and, very occasionally, La Nina, the IOD can have stronger or lesser impacts on the Indian monsoon.

FAQs

Q1: What is the Indian Ocean Dipole (IOD)?

Q2: How does a positive IOD affect Indian monsoons?

Q3: What happens during a negative IOD?

Q4: When was the IOD first discovered?

Q5: How is IOD different from El Niño?

MCQs

1. What is a characteristic of a positive IOD event?

a) Warm waters in the eastern Indian Ocean

b) Drought in Australia

c) Increased rainfall in Indonesia

d) Weakening of the monsoon in India

2. Which year witnessed a strong positive IOD event that significantly affected India’s rainfall?

a) 2005

b) 1997

c) 2019

d) 2011

3. How does IOD impact El Niño’s effect on India’s monsoon?

a) Amplifies El Niño

b) Has no impact

c) Counteracts El Niño

d) Exacerbates droughts

4. In which part of the ocean does the Indian Ocean Dipole primarily occur?

a) North Atlantic Ocean

b) Eastern Pacific Ocean

c) Indian Ocean

d) Arctic Ocean

5. What is the usual interval for the IOD cycle?

a) Every 2-3 years

b) Every 10 years

c) Annual

d) Every 5 years

GS Mains Questions and Model Answers

Q1: Explain how the Indian Ocean Dipole (IOD) influences the Indian monsoon.

Answer: The IOD has a significant impact on the Indian monsoon. A positive IOD, with warmer waters in the western Indian Ocean, enhances monsoon rainfall by driving moisture-laden winds towards India. Conversely, a negative IOD leads to warmer waters near Australia, resulting in dry conditions and deficient rainfall in India. The IOD’s interaction with other climatic phenomena, like El Niño, can amplify or mitigate monsoon patterns. Its impact highlights the interconnectedness of oceanic events with regional weather systems, crucial for India’s agriculture and economy.

Q2: Discuss the role of IOD in climate variability in the Indian Ocean region.

Answer: The IOD contributes to climate variability by affecting rainfall patterns, temperatures, and cyclonic activity across the Indian Ocean region. Positive IOD events cause heavy rains in East Africa and droughts in Australia, while negative events trigger the opposite patterns. The IOD also influences the frequency and intensity of tropical cyclones. As climate change progresses, understanding the IOD’s role becomes vital for forecasting and managing its impact on agriculture, fisheries, and water resources in the affected areas.

Q3: Evaluate the challenges in predicting the Indian Ocean Dipole and its impact on weather forecasting.

Answer: Predicting the IOD poses challenges due to its irregular occurrence and interactions with other climatic phenomena, such as the El Niño-Southern Oscillation (ENSO). Accurate forecasting requires sophisticated models that integrate ocean-atmosphere dynamics, but limited observation data from remote ocean regions hampers predictions. Improving technology, enhancing satellite data, and fostering international collaboration are essential for better forecasting. A more accurate understanding of IOD behavior can help mitigate the impact of extreme weather events on agriculture, fisheries, and water management.

Previous Year Questions on  Indian Ocean Dipole

1. UPSC CSE 2017

Question: "What is the Indian Ocean Dipole (IOD)? Explain its significance for the Indian monsoon." 

Answer: The IOD refers to the difference in sea surface temperatures between the western and eastern Indian Ocean. A positive IOD, with warmer waters in the west, strengthens the monsoon by bringing more rainfall to India. A negative IOD has the opposite effect, leading to deficient rainfall and drought conditions. The IOD’s role becomes particularly significant in years with El Niño, as a positive IOD can offset El Niño’s adverse impact on the monsoon. This phenomenon plays a crucial role in shaping agricultural productivity and water availability in India.

2. UPSC CSE 2020

Question: "How do oceanic phenomena like IOD and ENSO influence the Indian monsoon?" 

Answer: Both IOD and ENSO play critical roles in modulating the Indian monsoon. ENSO events in the Pacific Ocean, such as El Niño, typically lead to weaker monsoons and droughts in India. However, a positive IOD can counterbalance this effect by bringing more moisture to the subcontinent. On the other hand, a negative IOD can exacerbate drought conditions caused by El Niño. These interactions highlight the complexity of monsoon dynamics and the need for comprehensive forecasting models to predict seasonal rainfall accurately.