Larger Pacific Climate Event Helps Current La Nina Linger

Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

Image Advisory: 2008-066 April 21, 2008

Larger Pacific Climate Event Helps Current La Nina Linger

PASADENA, Calif. -- Boosted by the influence of a larger climate event in the Pacific, one of
the strongest La Ninas 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.

The new image is available online at:
http://sealevel.jpl.nasa.gov/science/jason1-quick-look/2008/images/20080401P.jpg .

This La Nina, 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 Nina 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: http://jisao.washington.edu/pdo/ and http://www.esr.org/pdo_index.html .

A La Nina is essentially the opposite of an El Nino. During El Nino, 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 Nina, 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 Nina changes global weather patterns and is
associated with less moisture in the air, and less rain along the coasts of North and South
America.

"This multi-year Pacific Decadal Oscillation 'cool' trend can intensify La Nina or diminish El
Nino 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 Nina 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:

http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif .

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 Nino, La Nina 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:

http://sealevel.jpl.nasa.gov/ ; or to view the latest Jason data, visit:

http://sealevel.jpl.nasa.gov/science/jason1-quick-look/ .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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