The Indian Ocean Dipole (IOD) is a phenomenon characterized by sustained changes in sea surface temperature differences between the western and eastern tropical Indian Ocean. A positive IOD phase occurs when temperatures in the western Indian Ocean are warmer than usual and temperatures in the eastern Indian Ocean are cooler than usual. This leads to drought conditions in Indonesia and heavy rainfall and flooding in eastern Africa. The intensity of the IOD is represented by the Dipole Mode Index (DMI), which measures the anomalous sea surface temperature gradient between the western and eastern tropical Indian Ocean. While the IOD and El Niño Southern Oscillation (ENSO) are both ocean-atmosphere coupled phenomena, they are independent of each other.

1. Indian Ocean Dipole
Presented by : Girish Patidar and Soumya Satyakant, SEOCS IIT Bhubaneswar

2. Indian Ocean Dipole (IOD)
• Sustained changes in the difference between sea surface
temperatures of the tropical western and eastern Indian Ocean.

3. phase of IOD

4. Why we are worried about IOD ?
The discovery of the dipole mode in Indian Ocean which
accounts for about 12% of the sea surface temperature
variability in the Indian Ocean and in its active years, also
causes severe rainfall in eastern Africa and droughts in
Indonesia and vice versa-brightens the prospects for a long-
term forecast of rainfall anomalies in the affected countries.

5. Dipole Mode Index (DMI)
• Intensity of the IOD is represented by anomalous SST gradient between
the western equatorial Indian Ocean (50E-70E and 10S-10N) and the
south eastern equatorial Indian Ocean (90E-110E and 10S-0N).
• This gradient is named as Dipole Mode Index (DMI).
• When the DMI is positive then, the phenomenon is refereed as the
positive IOD .

6. Is there any relation between IOD and ENSO ?
The answer is big NO both ENSO and IOD both are
ocean-atmosphere coupled phenomenon but both
are independent of each other.

8. IOD Oscillation cycle

9. Impact of IOD
• When the Dipole Mode Index (DMI) is positive it, leads to drought
over the Indonesian region and heavy rains and floods over the east
Africa.
• Saji et. Al. 1999 found the correlation between the IOD and ISMR(
Indian Summer Monsoon Rainfall) as .32 and claimed that the
relationship is not clear but according to Ashok et. Al 2001, 11
intense positive IOD events occurs during 1958-1997 out of which 8
events correspond with the positive anomalies of the ISMR.

10. References
• Ashok, K., Guan, Z. and Yamagata, T., 2001. Impact of the Indian
Ocean dipole on the relationship between the Indian monsoon
rainfall and ENSO. Geophysical Research Letters, 28(23), pp.4499-
4502.
• Marchant, R., Mumbi, C., Behera, S. and Yamagata, T., 2007. The
Indian Ocean dipole–the unsung driver of climatic variability in East
Africa. African Journal of Ecology, 45(1), pp.4-16.
• Saji, N.H., Goswami, B.N., Vinayachandran, P.N. and Yamagata, T.,
1999. A dipole mode in the tropical Indian Ocean. Nature, 401(6751),
p.360.