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La Niña hangs on
March 10, 1999
The cold pool of water in the Pacific known as "La Niña"
still persists, although it is slowly weakening, according to
scientists studying new data from the U.S.-French TOPEX/Poseidon
satellite.
It shows sea-surface height on
February 27, 1999 relative to normal ocean conditions, reflecting
the heat content of the ocean.
The low sea level or cold pool of water along the equator
(shown in purple and blue), commonly referred to as La Niña,
still dominates the equatorial Pacific Ocean. This La Niña,
which first appeared in May through June 1998, still persists,
although it is slowly weakening, scientists say. Given its
persistence and present strength, the ocean cooling trend is
expected to continue to exert a strong influence on global
climate systems throughout the spring and into the early summer.
This situation is similar to the 1997-1998 El Niño, which
extended into early summer 1998.
The world's oceans are the great reservoirs of heat that
influence global climate because they can cool or heat the
atmosphere above. This transfer of heat drives weather patterns
across both land and sea. La Niña provides a physical link
connecting the large, slow changes in the ocean with predictable
changes in day-to-day weather.
"La Niña shifts the high-altitude weather highway known as
the 'jet stream,'" said Dr. William Patzert, an oceanographer at
NASA's Jet Propulsion Laboratory. "It funnels storm tracks to the
Pacific Northwest, which has resulted in heavy rainfall and lots
of snow in that region so far, as well as the upper Midwest. Much
of the Southwest, by contrast, has been shielded from stormy
weather and, as a result, has received significantly less
precipitation than normal to date.
"This year's La Niña was average in its intensity, but at
its peak, it was associated with a 15- to- 20-centimeter deep
trough (6 to 8 inches) in the central tropical Pacific," Patzert
said. "The depression was correlated with a 2- to- 3-degree
Centigrade (about 3.5 to 5.5 degrees Fahrenheit) dip in normal
ocean surface temperatures."
The image also shows that the very large, unusual area of
higher or warmer water (shown here in red and white) in the
western Pacific Ocean, from the tropics to the Gulf of Alaska,
continues to expand. Although the appearance of this feature is
not fully understood, it is recognized as influential to overall
weather and climate.
The white areas in the image indicate that the sea-surface
height is between 14 and 32 centimeters (6 to 13 inches) above
normal; in the red areas, sea-surface height is about 10
centimeters (4 inches) above normal. The green areas indicate
normal conditions. The purple areas are between 14 to 18
centimeters (6 to 7 inches) below normal, and the blue areas are
between 5 to 13 centimeters (2 to 5 inches) below normal.
The TOPEX/Poseidon mission is managed by the Jet Propulsion
Laboratory for NASA's Office of Earth Science, Washington, DC.
JPL is a division of the California Institute of Technology,
Pasadena, CA.
For more information, please visit the TOPEX/Poseidon project
web page at
http://topex-www.jpl.nasa.gov/
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