MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Mary Hardin, (818) 354-0344
FOR IMMEDIATE RELEASE
June 26, 1998
NEW SATELLITE DATA SHOW RETREAT OF EL NIÑO, PACIFIC OCEAN IN
TRANSITION
New sea surface height measurements taken by the ocean-
observing TOPEX/Poseidon satellite show the equatorial Pacific in
a state of flux with the warm, high sea level El Niño-spawned
waters in retreat and areas of colder, low sea level waters on
the increase.
"Sea level is a measure of the heat stored in the ocean. In
the last month or so, the tropical Pacific has been switching
from warm to cold. Lower sea level indicates less heat, hence a
colder ocean," said Dr. Lee-Lueng Fu, the project scientist for
the U.S.-French TOPEX/Poseidon mission at NASA's Jet Propulsion
Laboratory, Pasadena, CA. "It appears now the central equatorial
Pacific ocean will stay colder than normal for some time to come
because sea level is about 18 centimeters (7 inches) below
normal, creating a deficit in the heat supply to the surface
waters. It is not clear yet, however, if this current cooling
trend will eventually evolve into a long-lasting La Niña
situation."
An El Niño condition begins when steady westward blowing
trade winds weaken and even reverse direction. This change in the
winds allows a large mass of warm water that is normally located
near Australia to move eastward along the equator until it
reaches the coast of South America.
This displaced pool of unusually warm water affects
evaporation, where rain clouds form -- and, in turn, alters the
typical atmospheric jet stream patterns around the world. The
change in the wind strength and direction also impacts global
weather patterns. The climatic event has been given the name El
Niño, a Spanish term for "the Christ child," because the warm
current first appeared off the coast of South America around
Christmas.
The 1997-98 El Niño has been the strongest ever recorded.
This phenomenon was responsible for record rainfall amounts in
California, heavy flooding in Peru, drought and wildfires in
Indonesia, tornadoes in the southeast United States and loss of
life and property damage worldwide. TOPEX/Poseidon's sea surface
height measurements have provided scientists with their first
detailed view of how El Niño's warm pool behaves because the
satellite measures the changing sea surface height with
unprecedented precision.
A "La Niña" (Spanish for "little girl") 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.
"It maybe too soon to say 'good-bye' El Niño and 'hello' La
Niña, because the effects of El Niño will remain in the climate
system for a long time," said Dr. Bill Patzert, a research
oceanographer at JPL. "However, if the Pacific is transitioning
to a La Niña, we'd expect to see clear, strong indication of it
by late summer or early fall -- in approximately August or
September -- just like we did last year with El Niño. The
strongest impacts of a potential La Niña wouldn't be felt in the
U.S. until next winter." A La Niña doesn't automatically follow
an El Niño, Patzert said.
Developed by NASA and the Centre National d'Etudes Spatiales
(CNES), the TOPEX/Poseidon satellite uses an altimeter to bounce
radar signals off the ocean's surface to get precise measurements
of the distance between the satellite and the sea surface. These
data are combined with measurements from other instruments that
pinpoint the satellite's exact location in space. Every 10 days,
scientists produce a complete map of global ocean topography, the
barely perceptible hills and valleys found on the sea surface.
Ocean temperatures affect ocean topography, which is why the
TOPEX/Poseidon radar altimeter is able to monitor the changing El
Niño and La Niña conditions. With detailed knowledge of ocean
topography, scientist can then calculate the speed and direction
of worldwide ocean currents.
The new satellite image from June 14 is available at:
http://www.jpl.nasa.gov/elnino/
JPL, a division of the California Institute of Technology,
manages the TOPEX/Poseidon mission for NASA's Earth Science
Enterprise, Washington, D.C.
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6-26-98 MAH
#9866
Note to Editors: A NASA TV video file featuring new animation
showing the entire 1997-98 El Niño event -- from December 1996 to
June 1998 -- will air at 9 a.m., noon, 3 p.m., 6 p.m. and 9 p.m.
Pacific Daylight Time on Friday, June 26. NASA TV is available
at GE-2, transponder 9C, 85 degrees west longitude, vertical
polarization, frequency 3880.0 megahertz, audio 6.8 megahertz.