- US physicists studying the El Niño and La
Niña
climate effects believe that these phenomena may simply be short-term
fluctuations
in a longer-lasting 'super-Niño' event. David Douglass and
colleagues
of the University of Rochester and David Clader at the State University
of New York at Geneseo have shown that climate data collected on El
Niño
and La Niña since 1967 closely fit a 'resonant function' with a
period of about 15 years. The researchers hope their discovery will help
climate experts to identify the geophysical mechanisms that underpin El
Niño and La Niña (arXiv.org/abs/physics/0203016).
-
- El Niño and La Niña are alternating hot
and cold periods in the atmosphere and ocean of the Pacific, each lasting
about six months. These effects are monitored by the 'sea surface
temperature
anomaly' - the deviation in the temperature of a certain region of the
Pacific ocean from its average temperature. El Niño and La
Niña
are defined as a difference of more than 0.4 degrees centigrade that lasts
at least five months. The 'southern oscillation index' - the difference
in atmospheric pressure between certain points in the Pacific - is also
closely linked to El Niño and La Niña.
-
- Climatologists had previously noticed that adjacent El
Niños and La Niñas had similar intensities. This prompted
Douglass' team to study these effects over a longer period, and they
gathered
measurements of the sea surface temperature anomaly and the southern
oscillation
index spanning more than 30 years.
-
- The researchers showed for the first time that the
intensities
of both El Niños and La Niñas went through a cycle lasting
about 15 years, which consisted of a large peak and two successively
smaller
peaks. Douglass - whose background is in condensed matter physics - and
co-workers realised that this pattern very closely matched a so-called
Landau-Lifshitz function, an equation that describes many damped resonant
systems in physics.
-
- The Landau-Lifshitz function predicted many features
of the super-Niño event detected in the climate data, together with
some that have not been seen yet. The physicists - who point out that they
are not climate experts - believe that climatologists could use these
results
to establish the nature of the force that drives the oscillations, and
to predict forthcoming El Niños and La Niñas.
-
- Douglass and colleagues based their study on data
collected
up to July 2000, and initially estimated the error of their model to be
between 30% and 50%. But they have been encouraged by more recent data
collected while they were writing their research paper, which closely fits
their original predictions.
-
- The physicists became involved in the study of El
Niño
while they were investigating how changes in the output of the Sun affect
the Earth's temperature. "The El Niño effects are 'noise' that
has to be removed," Douglass told PhysicsWeb. "What was
understood
about El Niño was not good enough for us so we advanced the
understanding
ourselves."
-
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