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Satellite shows Pacific running hot and cold
September 23, 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 September 12, 1998; these
sea surface heights are an indicator of the changing amount of
heat stored in the ocean. The tropical Pacific Ocean continues
to exhibit the complicated characteristics of both a lingering El
Nino, and a possibly waning La Nina situation. This image shows
that the rapid cooling of the central tropical Pacific has slowed
and this area of low sea level (shown in purple) has decreased
slightly since last month. It is still uncertain, scientists
say, that this cold pool will evolve into a long-lasting La Nina
situation. Remnants of the El Nino warm water pool, shown here
in red and white, are still lingering to the north and south of
the equator. The coexistence of these two contrasting conditions
indicates that the ocean and the climate system remain in
transition. These strong patterns have remained in the climate
system for many months and will continue to influence weather
conditions around the world in the coming fall and winter. The
satellite's sea-surface height measurements have provided
scientists with a detailed view of the 1997-98 El Nino because
the TOPEX/Poseidon satellite measures the changing sea-surface
height with unprecedented precision. The purple areas are about
18 centimeters (7 inches) below normal, creating a deficit in the
heat supply to the surface waters. 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 Nino 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 Nina situation is essentially the
opposite of an El Nino condition, but during La Nina 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 Nina situation also changes global
weather patterns, and is associated with less moisture in the air
resulting in less rain along the west coasts of North and South
America.
For more information, please visit the TOPEX/Poseidon project
web page at
http://topex-www.jpl.nasa.gov/
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