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Satellite image shows Pacific stablizing
July 16, 1998
This image of the Pacific Ocean was produced using sea-surface
height measurements taken by the U.S.-French TOPEX/Poseidon
satellite. The image shows sea surface height relative to normal
ocean conditions on July 11, 1998; sea surface height is an
indicator of the heat content of the ocean. The purple area in
the center of the image is a pulse of cold water moving across
the equator which the satellite measures as a region of lower
than normal sea level. This image shows that the rapid cooling of
the central tropical Pacific has stabilized and this area of low
sea level has stayed in about the same place since mid-June. The
purple areas are about 18 centimeters (7 inches) below normal,
creating a deficit in the heat supply to the surface waters. It
is not certain yet, if this current cooling trend (shown in
purple) will eventually evolve into a long-lasting La Niña
situation. Remnants of the El Niño warm water pool, shown here in
red and white, are still lingering to the north and south of the
equator in the center of this image. The effects of El Niño can
remain in the climate system for a long time and could still
impact weather conditions around the world. The satellite's sea-
surface height measurements have provided scientists with a
detailed view of the 1997-98 El Niño because the TOPEX/Poseidon
satellite measures the changing sea-surface height with
unprecedented precision. In this image, the white areas show the
sea surface is between 14 and 32 centimeters (6 to 13 inches)
above normal; in the red areas, it's about 10 centimeters (4
inches) above normal. The green areas indicate normal conditions.
The purple areas are 14 to 18 centimeters (6 to 7 inches) below
normal and the blue areas are 5 to 13 centimeters (2 to 5 inches)
below normal. The El Niño phenomenon is thought to be triggered
when the steady westward blowing trade winds weaken and even
reverse direction. This change in the winds allows a large mass
of warm water (the red and white area) that is normally located
near Australia to move eastward along the equator until it
reaches the coast of South America. The displacement of so much
warm water affects evaporation, where rain clouds form and,
consequently, alters the typical atmospheric jet stream patterns
around the world. A La Niña situation is essentially the opposite
of an El Niño condition, where the trade winds are stronger than
normal and the cold water that normally exists along the coast of
South America extends to the central equatorial Pacific. A La
Niña situation also changes global weather patterns, and is
associated with less moisture in the air resulting in less rain
along the coasts of North and South America. TOPEX/Poseidon will
be able to track a potentially developing La Niña with the same
accuracy.
For more information, please visit the TOPEX/Poseidon project
web page at
http://topex-www.jpl.nasa.gov/
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