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A giant horseshoe pattern of higher than normal sea-surface
heights developing over the last year is beginning to dominate
the entire western Pacific and Asiatic oceans, new imagery from
the U.S.-French TOPEX/Poseidon satellite shows.

Scientists at NASA’s Jet Propulsion Laboratory, Pasadena,
Calif., studying the new data believe these abnormally warm ocean
temperatures, which contrast with a cool La NiNa, may be part of
a larger, longer-lasting climate pattern.

The latest data, taken December 30, 1999 through January 8,
2000, show that this slower-developing condition covers most of
the Pacific Ocean and has significant implications for global
climate change, especially over North America, said Dr. William
Patzert, an oceanographer at JPL.

“In contrast with the more spectacular but shorter duration
El NiNo and La NiNa events, this multiple-year trend may be part
of a decade-long pattern known as the ‘Pacific decadal
oscillation,'” Patzert said. “The persistence of these abnormally
high and low Pacific sea-surface patterns, along with warmer and
colder than average ocean temperatures, tells us there is much
more than an isolated La NiÒa occurring in the Pacific Ocean.”

Satellite data from the National Oceanic and Atmospheric
Administration clearly illustrate the pattern. Sea-surface
temperatures, which directly affect the atmosphere on a daily
basis, are available at , and
show the same warm and cool water patterns.

“These warmer and cooler than normal sea-surface
temperatures influence our atmosphere every day, while sea-
surface heights are a measure of how much heat is stored in the
ocean below,” Patzert said. “When you put these two pieces of the
climate puzzle together, they will tell us both about what is
influencing today’s weather and how much heat is being stored in
the ocean to fuel future planetary climate events.”

The Pacific decadal oscillation waxes and wanes
approximately every 20 to 30 years, alternating between its
present phase, with a warm horseshoe pattern of higher than
normal sea-surface heights connecting the north, west and
southern Pacific, in contrast to a cool wedge of lower than
normal sea-surface heights in the eastern equatorial Pacific.
After that the Pacific switches to the opposite phase, showing a
reversal of the warm and cool regions; the horseshoe becomes cool
and the wedge warms.

The strength of this climate trend is seen in the current
TOPEX/Poseidon satellite image, available at . Sea-surface height is shown
relative to normal (green) height and reveals cooler water (blue
and purple) measuring between 8 and 24 centimeters (3 and 9
inches) lower than normal along the coast of Central and South
America, and stretching out into the equatorial Pacific. The
giant horseshoe of warmer water (red and white) dominating the
western and mid-latitude Pacific has higher than normal sea-
surface heights of between 8 and 24 centimeters (3 and 9 inches).
For the past year, warmer waters have been expanding slowly and
are now beginning to dominate the western and north Pacific.

Although it is too early to definitively label these basin-
wide conditions as a strong, multiple-year Pacific decadal
oscillation, the current image suggests that simple labels or
explanations such as a continuing La Nina/El Nino climate
condition could be misleading, Patzert said. In the coming year,
scientists using TOPEX/Poseidon data will continue to monitor the
development of these conditions and their implications for
climate in the next several years.

The U.S.-French TOPEX/Poseidon mission is managed JPL for
the NASA’s Earth Science Enterprise, Washington, D.C. JPL is a
division of the California Institute of Technology in Pasadena.


01/19/2000 DEA