The Indian Ocean Dipole (IOD), also known as the Indian Niño, is an irregular oscillation of sea-surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean. (Wikipedia)

The IOD phenomenon was first identified by climate researchers in 1999 by Dr. Saji et al.

The name ” Indian Ocean Dipole (IOD) ” was coined by Prof. Yamagata, Dr. Saji and other researchers of the Climate Variations Research Program (CVRP) of Frontier Research Center for Global Change (FRCGC) to represent the zonal dipole structure of the various coupled ocean-atmosphere parameters such as SST, OLR and Sea Surface Height anomalies. Generally, this configuration is also called positive IOD. Infact, a negative IOD also evolves preceding/following a positive IOD, with reverse in the configuration of the positive IOD. (JAMSTEC)

The Indian Ocean Dipole (IOD) is a coupled ocean-atmosphere phenomenon in the Indian Ocean. It is normally characterized by anomalous cooling of SST in the south eastern equatorial Indian Ocean and anomalous warming of SST in the western equatorial Indian Ocean. Associated with these changes the normal convection situated over the eastern Indian Ocean warm pool shifts to the west and brings heavy rainfall over the east Africa and severe droughts/forest fires over the Indonesian region. (JAMSTEC)

Schematic of a positive IOD event. Schematic of a negative IOD event.
Schematic of a positive IOD event Schematic of a negative IOD event.

SST anomalies are shaded (red color is for warm anomalies and blue is for cold). White patches indicate increased convective activities and arrows indicate anomalous wind directions during IOD events. (JAMSTEC)

 

Neutral IOD phase

Water from the Pacific flows between the islands of Indonesia, keeping seas to Australia’s northwest warm. Air rises above this area and falls over the western half of the Indian Ocean basin, blowing westerly winds along the equator.

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Indian Ocean Dipole Neutral Phase (Picture courtesy of BOM)

Positive IOD phase

Westerly winds weaken along the equator allowing warm water to shift towards Africa. Changes in the winds also allow cool water to rise up from the deep ocean in the east. This sets up a temperature difference across the tropical Indian Ocean with cooler than normal water in the east and warmer than normal water in the west.

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Indian Ocean Dipole Positive Phase (Picture courtesy of BOM)

 

Negative IOD phase

Westerly winds intensify along the equator, allowing warmer waters to concentrate near Australia. This sets up a temperature difference across the tropical Indian Ocean, with warmer than normal water in the east and cooler than normal water in the west.

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Indian Ocean Dipole Negative Phase (Picture courtesy of BOM)

Year of IOD

Year of IOD (Picture courtesy BOM)

One of the Strongest positive Indian Ocean Dipole recorded was during year 2006. However, the current development of IOD in 2019 seems will become more severe than the 2006 event.

Below are the IOD Index or Dipole Mode Index (DMI) from Dr. Saji IOD Homepage at http://enformtk.u-aizu.ac.jp/

How strong is the 2019 IOD?

mon_dmi-1c6ab921
A plot of monthly DMI from Jan 1998 to Aug 2019. The strongest event prior to 2019 in this plot is 2006. (by Dr. Saji Hameed)
dmi_06_19-f214d69c
A plot of daily DMI, WIN, and EIN from 01 Jan 2006 to 31 Aug 2019 is compared to the same quantities during 2006 (by Dr. Saji Hameed)

Impact of Positive IOD

Impact of Positive Indian Ocean Dipole around Asia and Africa region (Picture courtesy UNU)

 

To get scientific data on the IOD, you can visit to the IOD Page of Dr. Saji Hameed

IOD Data

Real Time IOD Monitoring

 

Reference:

Wikipedia, https://en.wikipedia.org/wiki/Indian_Ocean_Dipole

BOM, http://www.bom.gov.au/climate/iod/

JAMSTEC, http://www.jamstec.go.jp/aplinfo/sintexf/e/iod/about_iod.html

UNU, https://ourworld.unu.edu/en/indonesia-drought-kenya-flooding

Dr. Saji Hameed, http://enformtk.u-aizu.ac.jp/