The
Indian cousin of El Niño:
The second climatic problem
child
4
April, 2014
Floods
in East Africa and India, as well as drought and fires in Australia,
are periodic catastrophes caused by a second climate disruptor less
well known than its cousin El Niño: the Indian Ocean Dipole.
A new
study that made the cover of Nature
Geoscience,
involving a researcher from the LOCEAN laboratory (IRD, UPMC, CNRS,
MNHN) and various partners, shows that this recently developed
phenomenon affects the climate in this part of the world. The
researchers also show that the phenomenon has been occurring more
frequently over the past 30 years. The number of extreme
meteorological events that it causes should continue to increase in
the coming years due to climate change.
A
climate disruptor that is still misunderstood
Highlighted
several years ago, the phenomenon called "the Indian Ocean
Dipole" is a difference in temperatures between the surface
waters in the West and East of this ocean. Like "El Niño"
and its colder twin "La Niña" in the Pacific ocean, the
Indian ocean dipole fluctuates every 3 to 8 years between
"negative," "positive," and "neutral"
phases. The new study shows that the oceanic anomalies induced, like
those in the Pacific, periodically disrupt the climate in the Indian
Ocean region by promoting extreme meteorological events.
Droughts
in the East and Floods in the West
During
the positive phases of the Indian Ocean Dipole, the western part of
the ocean is colder than normal, while the eastern part is warmer.
This surface water temperature anomaly changes atmospheric
circulation. In the east, it reduces atmospheric convection (the
rise of hot, humid air) and reduces precipitation. In the west,
conversely, it increases convection. Moreover, this change in
convection accelerates the trade winds along the equator, which
causes colder deep water to rise and reinforces the temperature
contrast between the two sides of the ocean. The positive phase of
the Indian Ocean Dipole thus tends to cause droughts in East Asia
and Australia, and, on the contrary, floods in some parts of the
Indian subcontinent and East Africa.
Increasingly
frequent events
Through
the analysis of oceanic and climatic observations and to complex
computer simulations on data going back to the middle of the
19th century, the researchers also showed that the
positive phases have been increasingly frequent over the past 30
years. According to the study, this increased frequency is due to
warming of the tropical zone of the Indian Ocean that occurs more
rapidly in the west than in the east, in part due to the greenhouse
effect or to the rising atmospheric temperature. The researchers
identified a record number of eleven positive dipolar events since
the 1980s. This frequency is predicted to increase further in the
decades to come with the constant rise in surface temperature of
Earth.
This
work will help better predict the extreme climatic events that occur
in this part of the world and to better anticipate their
consequences. It will thus help governments and populations to
better prevent collateral damage such as major forest fires in
Southern Australia, the deterioration of the coral reefs west of the
island of Sumatra, or even the increase in floods and malaria
epidemics in East Africa.
Story
Source:
The
above story is based on materials provided
by Institut
de Recherche pour le Développement (IRD). Note:
Materials may be edited for content and length.
Journal
Reference:
- Wenju Cai, Xiao-Tong Zheng, Evan Weller, Mat Collins, Tim Cowan, Matthieu Lengaigne, Weidong Yu, Toshio Yamagata. Projected response of the Indian Ocean Dipole to greenhouse warming. Nature Geoscience, 2013; 6 (12): 999 DOI:10.1038/NGEO2009
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