The maps show a cross-sectional view of five-day-average temperature
in the top 300 meters* of the Pacific Ocean in mid-February, mid-March,
and mid-April 2014 compared to the long-term average (1981-2010).
Warmer than average waters are red; cooler than average waters are
blue.
Each map represents a 5-day average centered on the date shown.
From NOAA
The
El Niño /
La Niña climate pattern that alternately warms and
cools the eastern tropical Pacific is the 800-pound gorilla of Earth’s
climate system.
On a global scale, no other single phenomenon has a
greater influence on whether a year will be warmer, cooler, wetter, or
drier than average.
Naturally, then, the ears of seasonal forecasters
and natural resource managers around the world perked up back in early
March when NOAA’s Climate Prediction Center
issued an “El Niño Watch.”
The “watch” means that oceanic and atmospheric conditions in the tropical Pacific Ocean are favorable for the development of
El Niño
within the next six months.
These maps reveal one of the most
significant of those favorable signs: a deep pool of warm water sliding
eastward along the equator since late January.
The pool of warm water was lurking in the western Pacific in
mid-February, but it shifted progressively eastward in the subsequent
two months.
By mid-April, the unusually warm water was close to
breaching the surface in the eastern Pacific off South America.
NOAA
declares El Niño underway when the monthly average temperature in the
eastern Pacific is 0.5° Celsius or more above average.
Forecasts depending on different models
Such warm surface waters are unusual in the eastern Pacific because
the prevailing wind direction across the tropics is east to west: from
South America to Indonesia.
The easterly winds pile up sun-warmed
surface waters in the western Pacific like gusty winds build snow into
drifts.
Average sea level is literally higher in the western Pacific
than the eastern Pacific.
As the warm surface water is pushed westward by the prevailing winds,
cool water from deeper in the ocean rises to the surface near South
America.
This temperature gradient—warm waters around Indonesia and
cooler waters off South America—lasts only as long as the easterly winds
are blowing.
If those winds go slack or reverse direction in the western Pacific,
the warm pool of water around Indonesia is released and begins a slow
slosh back toward South America.
The slosh is called a
Kelvin wave.
If
the Kelvin wave has a strong impact on the surface waters in the central
and eastern Pacific, then it can help change the atmospheric
circulation and trigger a cascade of climatic side effects that
reverberate across the globe.
Will the odds of an El Niño event increase or decrease as summer
arrives?
How can one climate pattern have such a powerful effect on
weather far away?
For answers to these and other questions, keep an eye
out for a new blog planned for launch on
Climate.gov in coming weeks.
Produced by scientists from NOAA’s Climate Prediction Center and the
International Research Institute for Climate and Society, the blog will
follow the developing El Niño from the perspective of scientists at the
United States’ operational climate prediction center.
Links :
- Wired : If El Niño comes this year, it could be a monster
- NOAA : El Niño/Southern Oscillation (ENSO) Technical Discussion
