Pacific Decadal Oscillation Enhancing Current La Nina

“In fact,” said Willis, “these natural climate phenomena can sometimes
hide global warming caused by human activities. Or they can have the
opposite effect of accentuating it.”

Science Daily
Larger Pacific Climate Event Helps Current La Nina Linger

ScienceDaily (Apr. 22, 2008) – Boosted by the
influence of a larger climate event in the
Pacific, one of the strongest La Niñas in many
years is slowly weakening but continues to
blanket the Pacific Ocean near the equator, as
shown by new sea-level height data collected by
the U.S.-French Jason oceanographic satellite.

This La Niña, which has persisted for the past
year, is indicated by the blue area in the center
of the image along the equator. Blue indicates
lower than normal sea level (cold water). The
data were gathered in early April.

The image also shows that this La Niña is
occurring within the context of a larger climate
event, the early stages of a cool phase of the
basin-wide Pacific Decadal Oscillation. The
Pacific Decadal Oscillation is a long-term
fluctuation of the Pacific Ocean that waxes and
wanes between cool and warm phases approximately
every five to 20 years. In the cool phase, higher
than normal sea-surface heights caused by warm
water form a horseshoe pattern that connects the
north, west and southern Pacific, with cool water
in the middle. During most of the 1980s and
1990s, the Pacific was locked in the
oscillation’s warm phase, during which these warm
and cool regions are reversed. For an explanation
of the Pacific Decadal Oscillation and its
present state, see: and .

A La Niña is essentially the opposite of an El
Niño. During El Niño, trade winds weaken and warm
water occupies the entire tropical Pacific Ocean.
Heavy rains tied to the warm water move into the
central Pacific Ocean and cause drought in
Indonesia and Australia while altering the path
of the atmospheric jet stream over North and
South America. During La Niña, trade winds are
stronger than normal. Cold water that usually
sits along the coast of South America is pushed
to the middle of the equatorial Pacific. A La
Niña changes global weather patterns and is
associated with less moisture in the air, and
less rain along the coasts of North and South

“This multi-year Pacific Decadal Oscillation
‘cool’ trend can intensify La Niña or diminish El
Niño impacts around the Pacific basin,” said Bill
Patzert, an oceanographer and climatologist at
NASA’s Jet Propulsion Laboratory, Pasadena,
Calif. “The persistence of this large-scale
pattern tells us there is much more than an
isolated La Niña occurring in the Pacific Ocean.”

Sea surface temperature satellite data from the
National Oceanic and Atmospheric Administration
also clearly show a cool Pacific Decadal
Oscillation pattern, as seen at:
The shift in the Pacific Decadal Oscillation,
with its widespread Pacific Ocean temperature
changes, will have significant implications for
global climate. It can affect Pacific and
Atlantic hurricane activity, droughts and
flooding around the Pacific basin, marine
ecosystems and global land temperature patterns.

“The comings and goings of El Niño, La Niña and
the Pacific Decadal Oscillation are part of a
longer, ongoing change in global climate,” said
Josh Willis, a JPL oceanographer and climate
scientist. Sea level rise and global warming due
to increases in greenhouse gases can be strongly
affected by large natural climate phenomenon such
as the Pacific Decadal Oscillation and the El
Nino-Southern Oscillation. “In fact,” said
Willis, “these natural climate phenomena can
sometimes hide global warming caused by human
activities. Or they can have the opposite effect
of accentuating it.”

Jason’s follow-on mission, the Ocean Surface
Topography Mission/Jason-2, is scheduled for
launch this June and will extend to two decades
the continuous data record of sea surface heights
begun by Topex/Poseidon in 1992. JPL manages the
U.S. portion of the Jason mission for NASA’s
Science Mission Directorate, Washington, D.C.

For more information on NASA’s ocean surface
topography missions, see: ; or to view the
latest Jason data, visit:
Adapted from materials provided by NASA/Jet Propulsion Laboratory.

NASA/Jet Propulsion Laboratory (2008, April 22).
Larger Pacific Climate Event Helps Current La
Nina Linger. ScienceDaily. Retrieved April 22,
2008, from°© /releases/2008/04/080421195005.htm


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