What is the Indian Ocean Dipole? Explain its connection with the Indian monsoons

Mentors Comment:

The questions comes from the topic Salient Features of World’s Physical Geography. Its straight, to the point and nothing hidden in the question.

The first part of the question will address the concept and characteristics of IOD.

Then jump to the next requirement of the question where you have to discuss the role of IOD in Indian monsoon.

Here discuss the role of + IOD on normal rainfall, – IOD on drought like situation. Dont miss the relationship between IOD and El-Nino and how it affect each other.

One of the best way to score in these types of questions is to draw a diagram to show the phenomenon. It will be relatable to the examiner and you will score easy marks!

Model Answer:

Indian Ocean Dipole (IOD) is an atmosphere-ocean coupled phenomenon in the tropical Indian Ocean (like the El Nino is in the tropical Pacific), characterised by a difference in sea-surface temperatures.

Characteristics of IOD:

  • IOD is the difference between the temperature of eastern (Bay of Bengal) and the western Indian Ocean (Arabian Sea).
  • This temperature difference results into pressure difference which results in flowing of winds between eastern and western parts of Indian Ocean.
  • IOD develops in the equatorial region of Indian Ocean from April to May peaking in October.
  • A ‘positive IOD’ — or simply ‘IOD’ — is associated with cooler than normal sea-surface temperatures in the eastern equatorial Indian Ocean and warmer than normal sea-surface temperatures in the western tropical Indian Ocean.
  • The opposite phenomenon is called a ‘negative IOD’, and is characterised by warmer than normal SSTs in the eastern equatorial Indian Ocean and cooler than normal SSTs in the western tropical Indian Ocean

How does it impact the southwest monsoon?

  • Although El Nino Southern Oscillation [ENSO] was statistically effective in explaining several past droughts in India, in the recent decades the ENSO-Monsoon relationship seemed to weaken in the Indian subcontinent.
  • For e.g. the 1997, strong ENSO failed to cause drought in India.
  • It was later discovered that just like ENSO was an event in the Pacific Ocean, a similar seesaw ocean-atmosphere system in the Indian Ocean was also at play which was IOD.
  • However, there is no established correlation between Indian summer monsoon rainfall and IOD.
  • But, studies have shown that a positive IOD year sees more than normal rainfall over central India.
  • It was demonstrated that a positive IOD index often negated the effect of ENSO, resulting in increased Monsoon rains in several ENSO years like the 1983, 1994 and 1997.
  • Further, it was shown that the two poles of the IOD – the eastern pole (around Indonesia) and the western pole (off the African coast) were independently and cumulatively affecting the quantity of rains for the Monsoon in the Indian subcontinent.
  • The indicated connection is between below-normal SST in the eastern Indian Ocean and above-normal rain over central India, and vice versa.
  • A negative IOD, on the other hands, complements El NiNo leading to severe drought.
  • At the same time, Positive IOD results in more cyclones than usual in Arabian Sea.
  • Negative IOD results in stronger than usual cyclogenesis (Formation of Tropical Cyclones) in Bay of Bengal. Cyclogenesis in Arabian Sea is suppressed during this time.
  • But there is some anomaly in the phenomenon of IOD and Monsoon.


The cumulative effect of these factors along with ITCZ, absence of  Sub Tropical Westerly Jet (STWJ) is that a low pressure is created over the Indian subcontinent while a high pressure is formed in the Indian Ocean. This pushes the moist, rain bearing monsoon winds from the Arabian sea towards the subcontinent. The blockage of these winds by Western Ghats causes rains in the southern region while that by Himalayas leads to downpours over North India.

By Root

Caretaker @civilsdaily

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Harshal Deore
Harshal Deore
4 years ago

CD20385comment image comment image

Pritam Kumar
4 years ago
Reply to  Harshal Deore

Hi Harshal…
-Introduction is incomplete….IOD is not only oscillation in sea surface…but the temperature difference in ocean water (more or less than normal) affects the air circulation in atmosphere…this entire cycle in known as IOD…
-You haven’t mentioned much about its connection with Indian monsoon…only the 3rd last point talks about it that is also info…and not explaining in details…
We don’t need to discuss the type here…focus more to the demand of the question…
-There is no conclusion in answer…

However, You attempt is good…keep writing will improve for sure…
Marks awarded: 2.5/10

4 years ago

comment image

Pritam Kumar
4 years ago
Reply to  CD0705

Hello CD0705
-The answer is incomplete….You have mentioned in intro itself that its an atmospheric phenomena….however the following line does not mention how it affects atmosphere….monsoon etc…
-Also need to mention how it gets affected or affects ENSO…
-Its impact on Indian monsoon….idea mentioned here need more justification….
-No conclusion…
Overall its an below average answer….
Good attempt…keep writing…
Marks awarded: 2/10

Xshay Anil Wakhare
Xshay Anil Wakhare
4 years ago

CDTEST30897comment imagecomment image

Pritam Kumar
4 years ago

Hello…Xshay Anil
-Good introduction….with good flow of ideas…and arranged in well manner…good one…
-Very well established relationship…with clarity in words…
-However, the conclusion is absent…
-Under heading….IOD, La-Nina and El-Nino…some clarification needed…IOD is more like ENSO…Also need to mention how ENSO affects IOD and vice versa…and how Indian monsoon gets affected…
Though good attempt…keep writing…will improve for sure….
Marks awarded: 4/10

4 years ago

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Pritam Kumar
4 years ago
Reply to  hiddenwarrior

Hello Hiddenwarrior…
-Intro need more explanation…with more relevant points in it…
-You have established relationship…in general sense…though better…
-In conclusion….what sort of steps should be taken????? its more a natural phenomena….and occurs in some or other years…so human steps may be less relevant…though may prove a bit significance…but you need to be specific…by mentioning those points…

Good attempt…keep writing…
Marks awarded: 3/10

4 years ago

CDTEST 20378comment image

Pritam Kumar
4 years ago
Reply to  Invincible

Hello Invincible…
-Intro is okay….
-However, the relationship with monsoon is not established in well manner…You have mentioned about the consequences….and not the phenomena…However, the diagram talks about the phenomena but the relationship is absent…
-Also very limited points…shows answer is incomplete…
-No conclusion….
Well attempted…keep writing…

4 years ago

comment imagecomment image

Pritam Kumar
4 years ago
Reply to  Imgroot

Hello Imgroot
-Very good introduction….
-Good ideas…well arranged….and well written points…
-Well done…nice attempt…excellent answer…
-Need to bring conclusion…in a bit detail…
-Good one… keep writing…
Marks awarded: 5.5/10


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