PARIS—Weather experts say they have a tip that could give up to
14 months' warning before the onset of an El Niño, the weather
anomaly that whacks countries around the Pacific and affects
southern Africa and even Europe.
At present, scientists are unable to give little more than a few
months' notice that an El Niño is in the offing, which is often too
late for farmers, fishermen and others to prepare for weather
disruption.
El Niño occurs every two to seven years, when the trade winds
that circulate surface water in the tropical Pacific start to
weaken.
A mass of warm water builds in the western Pacific and eventually
rides over to the eastern side of the ocean.
The outcome is a major shift in rainfall, bringing floods and
mudslides to usually arid countries in western parts of South
America and drought in the western Pacific, as well as a change in
nutrient-rich ocean currents that lure fish.
El Niño is ushered out by a cold phase, La Niña, which usually
occurs the following year.
Meteorologists led by Takeshi Izumo of the Research Institute for
Global Change in Yokohama, Japan, believe the world can gain a
precious early warning from a similar event that occurs in the
Indian Ocean.
This oscillation, first identified in 1999, occurs roughly every
two years.
Analysis of weather records from 1981 to 2009 found that when the
so-called Indian Ocean Dipole was in a "negative" phase -- with the
waters warm in the west and cold in the east -- an El Niño event in
the Pacific followed more than a year later.
The driver for this pendulum appears to be a pattern in
atmospheric circulation linking the two oceans, Izumo believes.
The paper is published online on Sunday by the journal Nature
Geoscience.
In a commentary, Peter Webster and Carlos Hoyos, earth scientists
at the Georgia Institute of Technology, Atlanta, said that work was
needed to delve into the past.
The 1981-2009 period did indeed show a "strong two-year rhythm"
in which the Dipole swung along with El Niño.
Other research, based on sea temperatures from 1890-2008,
suggests the Indian Ocean pendulum may vary from decade to decade,
the pair cautioned.
