PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
Contact: Mary A. Hardin
National Oceanic and Atmospheric Administration
FOR IMMEDIATE RELEASEMay 29, 1997
COMPLEMENTARY SATELLITE MEASUREMENTS SUGGEST EL NIñO IS BREWING
Simultaneous ocean measurements taken by two orbiting NASA
science instruments suggest that another weather-disrupting El
Niño condition may be developing in the Pacific Ocean, with the
potential of altering global weather patterns next winter.
Sea-surface height measurements taken by the radar altimeter
onboard the joint U.S.-French TOPEX/POSEIDON satellite and wind
data collected by the NASA Scatterometer on Japan's Advanced
Earth Observing Satellite (ADEOS) are being used together for the
first time to diagnose changing oceanographic and atmospheric
conditions in the tropical Pacific Ocean.
The El Niño phenomenon is thought to be triggered when
steady westward blowing trade winds weaken and even reverse
direction. This change in the winds allows the 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
where rain clouds form and, consequently, alters the typical
atmospheric jet stream patterns around the world. The change in
the wind strength and direction also impacts global weather
"NSCAT has observed two episodes of the reversal of the
trade winds in the western Pacific, one at the end of December
and one at the end of February. Both generated warm water masses,
called Kelvin waves, that traveled across the Pacific and were
measured by TOPEX/Poseidon," said Dr. Lee-Lueng Fu,
TOPEX/Poseidon project scientist at NASA's Jet Propulsion
Laboratory, Pasadena, CA. "Kelvin waves are often a precursor to
a warm state of the tropical Pacific, sometimes leading to an El
"Whether an El Niño event will occur cannot be determined by
just examining the satellite data," Fu continued. "A computer
model that couples ocean-atmosphere data, like the one used by
the National Oceanographic and Atmospheric Administration (NOAA),
is a necessary tool to issue scientifically based predictions.
Now, for the first time, both TOPEX/POSEIDON and NSCAT are
observing and providing the best, near real-time view of global
ocean winds and sea level ever obtained. These observations will
help NOAA's model to predict the occurrence of El Niño."
NOAA has issued an advisory regarding the presence of the
early indications of El Niño conditions. A number of El Niño
forecast activities supported by NOAA indicate the likelihood of
a moderate or strong El Niño in late 1997. The forecast model
operated at NOAA's National Centers for Environmental Prediction
(NCEP) used data collected by the TOPEX/POSEIDON satellite.
"The use of TOPEX/POSEIDON data clearly improved our
forecast for the winter of 1996-1997," said Dr. Ants Leetmaa,
chief scientist at NCEP. "We currently use the data continuously
for our operational ocean analyses and El Niño forecasts. The
use of this data set enabled a clearer picture to be developed of
the multi-year evolution of ocean conditions in the tropical
Pacific that have resulted in the onset of the current warm
episode. We have not yet had a chance to utilize the NSCAT data
in the models but we anticipate that its use will also improve
our forecast system."
"Since the beginning of the instrument's operation in
September 1996, NSCAT has observed stronger than normal easterly
winds in the central and western tropical Pacific, which might
have piled up warm water in the west as indicated by the higher
than normal sea level and sea surface temperature," said Dr. W.
Timothy Liu, NSCAT project scientist at JPL. "This is usually a
precursor of subsequent anomalous warming in the east. Kelvin
waves moving across the Pacific do not necessarily mean El Niño,
but we are studying how these seasonal phenomena like Kelvin
waves are related to events like El Niño that occur over several
years. TOPEX/POSEIDON and NSCAT will provide continuous, near
real-time observations of the critical developments in the
Pacific in the months to come."
The climatic event has been given the name El Niño, a
Spanish term for a "boy child," because the warm current first
appeared off the coast of South America around Christmas. Past
El Niño events have caused unusually heavy rain and flooding in
California, unseasonably mild winters in the Eastern United
States and severe droughts in Australia, Africa and Indonesia.
Better predictions of extreme climate episodes like floods and
droughts could save the United States billions of dollars in
damage costs. El Niño episodes usually occur approximately every
two to seven years.
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. With detailed knowledge of ocean topography, scientist
can then calculate the speed and direction of worldwide ocean
The NASA scatterometer uses an array of stick-like antennas
that radiate radar pulses in the Ku-band across broad regions of
the Earth's surface. The way the radar signal bounces off the
ocean's surface allows scientists to calculate both wind speed
and direction. At any given time NSCAT's antennas scan two
swaths of ocean -- one oneither side of the satellite's near-
polar, sun-synchronous 500-mile (800-kilometer) orbit. The
scatterometer takes 190,000 wind measurements per day, mapping
more than 90 percent of the world's ice-free oceans every two
Both the TOPEX/POSEIDON altimeter and the NASA scatterometer
are radar instruments which allow them to operate 24 hours a day,
collecting data day or night, regardless of sunlight or weather
The following Internet sites can be accessed for
The Jet Propulsion Laboratory manages the TOPEX/POSEIDON
and NASA Scatterometer missions for NASA's Mission to Planet
Earth enterprise, Washington, DC.
NOTE TO EDITORS: A NASA TV Video File featuring TOPEX/Poseidon
animation of the Kelvin Wave moving across the Pacific Ocean,
plus an interview with Dr. Lee-Lueng Fu will air today, Thursday,
May 29 at 9 a.m., noon, 3 p.m., 6 p.m. and 9 p.m. Pacific Time.
NASA TV is broadcast on GE-2, transponder 9C, C-Band, located at
85 degrees West longitude. The frequency is 3880.0 MHz.
Polarization is vertical and audio is monaural at 6.8 MHz.