El Niño-Southern Oscillation
Average circulation in the south Pacific
Ocean
El Niño-Southern Oscillation (ENSO; com-
monly referred to as simply El Niño) is a
global coupled ocean-atmosphere phenomen-
on. The Pacific ocean signatures, El Niño
and La Niña are important temperature fluc-
tuations in surface waters of the tropical
Eastern Pacific Ocean. The name El Niño,
from the Spanish for "the little boy", refers to
the Christ child, because the phenomenon is
usually noticed around Christmas time in the
Pacific Ocean off the west coast of South
America.[1] La Niña, similarly, means "the
little girl". These effects were first described
in 1923 by Sir Gilbert Thomas Walker from
whom the Walker circulation, an important
aspect of the Pacific ENSO phenomenon,
takes its name. The atmospheric signature,
the Southern Oscillation (SO) reflects the
monthly or seasonal fluctuations in the air
pressure difference between Tahiti and Dar-
win, Australia. The most recent occurrence of
El Niño started in September 2006[2] and las-
ted until early 2007.[3] From June 2007 on,
data
indicated a weak La Niña event,
strengthening in early 2008 and weakening
in late 2008, with a forecast return to neutral
conditions in 2009.
ENSO is associated with floods, droughts,
and other disturbances in a range of loca-
tions around the world. These effects, and
the irregularity of the ENSO phenomenon,
makes predicting it of high interest. Signific-
ant advances in the predictability of ENSO
were contributed by Stephen Zebiak and
Mark Cane.[4] ENSO is the most prominent
known source of inter-annual variability in
weather and climate around the world (about
3 to 8 years), though not all areas are af-
fected. ENSO has signatures in the Pacific,
Atlantic and Indian Oceans.
During major warm events, El Niño warm-
ing extends over much of the tropical Pacific
and becomes clearly linked to the intensity of
the Southern Oscillation. While ENSO effects
are basically in phase between the Pacific
and Indian Oceans, ENSO effects in the At-
lantic Ocean lag