Saji N. Hameed & Toshio
Yamagata talk with ScienceWatch.com and answer a
few questions about this month's Emerging Research Front
Paper in the field of Environment &
Article: Possible impacts of Indian Ocean Dipole
mode events on global climate
Journal: CLIMATE RES, 25 (2): 151-169 DEC 5 2003
Addresses: Int Pacific Res Ctr, 2525 Correa Rd, Honolulu,
HI 96822 USA.
Inst Global Change Res, Kanazawa, Kanagawa 2360001,
Univ Tokyo, Dept Earth & Planetary Sci, Tokyo 1130033,
Why do you think your paper is highly
The discovery of an ocean-atmosphere coupled mode named the "Indian Ocean
Dipole mode" (IOD)—Saji NH, et al., "A dipole mode in the
tropical Indian Ocean," (Nature 401: 360-63, Sep 23
1999)—radically changed prevailing paradigms on the role of the
Indian Ocean in the world climate variability. Prior to that, most climate
scientists had written off the Indian Ocean just as a slave of the "king of
climate variations," i.e., El Niño Southern Oscillation (ENSO)
phenomenon in the adjoining tropical Pacific.
However, our 1999 work revealed that the Indian Ocean is capable of
generating its own climate mode, now known as IOD. For a while, after this
finding, the IOD was perceived to be a regional mode of climate variability
with impacts restricted to the Indian Ocean rim countries. Our work in 2003
objectively analyzed global climate variations associated with IOD and
demonstrated, for the first time, that it influences worldwide climate to a
more or less similar extent as ENSO.
Climate science is a very young discipline. In the last two or three
decades, major research and exploration had revolved around a few phenomena
such as ENSO. There is no doubt that ENSO has had a significant impact on
worldwide climate. However, it cannot consistently explain notable climatic
anomalies. This is partly because no El Niño is alike and hence the
impacts also differ.
El Niño is even changing within a changing climate as discussed in
Ashok K, et al., "El Niño Modoki and its possible
teleconnection," (Journal Of Geophysical Research-Oceans: 112:
C11007, 2007) and also in Weng HY, et al., "Impacts of recent El
Niño Modoki on dry/wet conditions in the Pacific rim during boreal
summer," (Climate Dynamics: 29[2-3]: 113-29, AUG 2007).
Another reason is that other climatic phenomena may play major yet unknown
roles. Our work revealed the previously unknown role of IOD. Some of the
impacts had been falsely attributed to ENSO because of some apparent
co-occurrences of IOD and ENSO. Therefore, we clarified, again for the
first time, the differential impacts of IOD and ENSO by use of the partial
correlation method. These efforts have brought a better understanding of
year-to-year climate variations and enhanced the predictability of climate
variations at seasonal time scales.
Another reason for the popularity of the work is due to the recent frequent
IOD activity in our changing climate system. The last few years have seen
three consecutive IODs—in 2006, 2007, and 2008—which is unheard
of in the previous 50 years of available historical records. It is also
revealed that the IOD is a major cause of the severe drought in Australia.
All these aspects are bringing more and more attention to the Indian Ocean
Dipole and its impacts.
Would you summarize the significance of your paper in
The paper discusses and reveals, for the first time, the possible climate
anomalies that are expected to happen during the duration of an IOD event.
Note that active IOD events can potentially generate worldwide climate
impacts lasting for a half-year period from June to November. The paper
also explores and addresses some critical issues regarding the relation
between IOD and ENSO.
During the first few years following the discovery of IOD, there was a
vigorous scientific debate on the relation between IOD and ENSO, with many
researchers considering that the IOD was a local climate fluctuation driven
by ENSO. This issue was well-explored in our analysis and we were able to
demonstrate that not only is IOD an independent phenomenon, but that it has
its own unique effect on worldwide climate.
How did you become involved in this research and were
any particular problems encountered along the way?
The discovery of the IOD was made while I was a postdoctoral fellow working
with Professor Toshio Yamagata at the University of Tokyo, at the then
Frontier Research System for Global Change (currently the Research
Institute for Global Change). Soon after I joined the group, in early 1998,
I became involved in some new work with another postdoctoral fellow, Dr.
P.N. Vinayachandran, now an Associate Professor in the Oceanography Centre
for Atmospheric and Oceanic Sciences at the Indian Institute of Science in
We were puzzled by an unusually strong oceanic event that had taken place
in the Indian Ocean in 1994. The year 1994 was a very strange year, with an
extremely hot summer in Japan, and Professor Yamagata had already begun an
investigation to identify its root cause.
Prof. Vinayachandran, a physical oceanographer by training, had noted an
unusual reversal of the direction of the so-called Wyrtki-Yoshida jet in
the ocean. This is a fast ocean surface current that moves from west to
east along the equatorial Indian Ocean during the boreal spring and fall
He noted that, in 1994, the jet was absent in spring and that by fall it
had reversed direction and was moving from east to west. On further
examination we found that the breakdown and subsequent reversal of the jet
were related to overlying changes in the atmosphere itself, especially in
the surface winds. After we solved this puzzle, we were faced with the
harder question of whether the event was a rare one, perhaps related to the
rapid global warming in the 90s.
I took our new exciting results with me on a trip to my alma mater in India
and discussed it with my thesis advisor, Professor B. N. Goswami, of the
Oceanography Centre for Atmospheric and Oceanic Sciences at the Indian
Institute of Science in Bangalore, India. At that time he had been
exploring several hypotheses to link surface current and temperature
variations in the Indian Ocean with the monsoons and was very interested in
Thus an inter-country, inter-institutional collaboration was born, and we
joined forces to attack the problem from all possible directions. After a
year of rigorous examination of a variety of available historical datasets,
we discovered that the phenomenon occurred at various times in the past
records and was definitely not a new kind of variability related to
possible changes in the climate system brought about by global warming.
We also constructed and examined various competing hypotheses to explain
the existence of these climate events. After careful analysis, often
accompanied by numerical experimentation, we ruled out all the hypotheses
except for one—that the event was driven by inherent air/sea
interactions in the Indian Ocean itself. The concept of IOD was born then
and there and I have been involved with this research ever since.
The concept of IOD as an independent phenomenon arising out of inherent
air/sea interactions within the Indian Ocean was not well accepted in the
beginning. As I mentioned earlier, it painted a picture of an active role
of the Indian Ocean in global climate variations that was radically
different from the prevailing ideas. It took a few years of scientific
debates and further explorations to establish the status of the IOD as an
independent forcing agent of global climate variations.
Where do you see your research leading in the
I have been interested in extending IOD research in several new directions.
One of the exciting works I am currently doing is looking at the
interaction between IOD and ENSO events. I am also very interested in
interdecadal modulations of the IOD. It has been noted that IOD activity is
strong in some decades and weak in others. For example, the 1960s and '70s
experienced a string of moderate to strong IOD events, the '80s experienced
only a single strong IOD event.
As I noted, the IOD activity has reemerged in the global climate system
since the mid '90s. While it is clear that there are decade to decade
changes in IOD activity, we need to understand why IOD is active in some
decades but not in others. Finally I am also interested in multiscale
interactions during IOD, for example how the intraseasonal activities
happening on the much shorter time scale of 30 to 70 days are modulated or
modulate the phenomenon.
Do you foresee any social or political implications for
Definitely. IOD events have a significant impact on worldwide temperatures
and rainfall. Through these variations it affects societies significantly,
perhaps mostly in developing or underdeveloped countries. The disastrous
consequences of severe floods that displaced nearly two million people in
East Africa and the severe drought that caused widespread wildfires in
Indonesia and Malaysia, besides triggering unprecedented haze in
neighboring countries during an IOD event in 2006, could have been managed
better if the event was predicted in advance and affected countries were
alerted to its possible impacts.
Also, the rapid rise of global wheat prices can be related to the droughts
of 2006, 2007, and 2008 in Australia, all of them coinciding with IOD
events during the same years. The ongoing efforts by several countries,
including Australia, India, Indonesia, Japan, and the USA to implement a
sustained climate observing network over the Indian Ocean is a testimony to
the fact that scientists and policymakers worldwide are beginning to
realize the practical importance of understanding and predicting IOD
Dr. Saji N. Hameed
Director of Science
APEC Climate Center
Prof. Toshio Yamagata, Dean
School of Science
The University of Tokyo
Tokyo, Japan Web