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Contact: Mary A. Hardin
FOR IMMEDIATE RELEASEApril 12, 1996
WEATHER-CHANGING OCEANS WAVES CHARTED FROM SPACE
New results from the ocean-observing TOPEX/Poseidon
satellite are challenging a fundamental oceanographic theory
about the speed of large-scale ocean waves -- a finding that
could ultimately revise science textbooks and improve global
The large-scale ocean waves, with wavelengths of hundreds
of kilometers from one wave crest to the next, are called Rossby
waves. These waves carry a "memory" of weather changes that
have happened at distant locations over the ocean, according to
Dr. Dudley Chelton, a TOPEX/Poseidon science team member at the
College of Oceanic and Atmospheric Sciences at Oregon State
University in Corvallis.
Using data gathered by the satellite, scientists
tracked the waves as they move through the open ocean and have
determined that, at mid-latitudes, the Rossby waves are moving
two to three times faster than previously thought, Chelton
reports in today's issue of Science magazine.
Rossby waves are a natural result of the Earth's rotation
and a key feature of large-scale ocean circulation. In
animations of altimeter data from the TOPEX/Poseidon satellite,
the waves appear as alternating positive and negative sea level
features traveling throughout much of the world oceans.
"Every first-year student in physical oceanography learns
about Rossby waves. However, observing them away from the Equator
has been extraordinarily difficult, because they cause changes in
sea level of 10 to 20 centimeters (4 - 8 inches), spread over
hundreds of kilometers, and move westward so slowly that a wave
may take more than 10 years to cross the Pacific at the latitude
of Los Angeles, and more than 30 years at the latitude of
Portland, Oregon," said Dr. Victor Zlotnicki, an oceanographer
at NASA's Jet Propulsion Laboratory.
"Thanks to TOPEX/Poseidon, for the first time we can see
these waves very clearly, and this research shows that they
become more intense to the west of the great mountain chains on
the ocean floor, and more fundamentally, that they travel much
faster than the accepted theory predicts," Zlotnicki said.
Since Rossby waves can alter currents and their
corresponding sea surface temperatures, the waves influence the
way the oceans release heat to the atmosphere and thus are able
to affect weather patterns.
For example, in 1994, oceanographers at the Naval Research
Laboratory mapped a Rossby wave that they concluded was a remnant
of the 1982-83 El Nino event. They found evidence that the
Kuroshio current, located off the coast of Japan, was pushed
northward, raising the temperature of the northwest Pacific.
Some scientists blamed this shift for contributing to the
flooding across the midwestern United States in 1993.
"If our traditional notions about the wave speeds
are incorrect," Chelton said, "then the waves get from one side
of the mid-latitude ocean to the other twice as fast, which means
that the ocean evidently adjusts more rapidly that we previously
This more precise information about how fast the
waves are traveling may help forecasters improve their ability to
predict the effects of El Nino events on weather patterns years
TOPEX/Poseidon, a joint program of NASA and the Centre
National d'Etudes Spatiales, the French space agency, uses a
radar altimeter to precisely measure sea-surface height.
Scientists use the TOPEX/Poseidon data to produce global maps of
ocean topography, which then can be used to identify Rossby
TOPEX/Poseidon is part of NASA's Mission to Planet Earth, a
coordinated, long-term research program to study the Earth as a
global system. TOPEX/Poseidon's sea-surface height data are
essential to a better understanding of the role oceans play in
regulating global climate, one of the least understood areas of
The Jet Propulsion Laboratory manages the U.S. portion of
the TOPEX/Poseidon mission for NASA.
NOTE: A NASA Television Video File will feature wave animation
produced by the TOPEX/Poseidon satellite and an interview with
JPL's Dr. Victor Zlotnicki, on Friday, April 12 at 9 a.m., Noon,
3 p.m. and 6 p.m. Pacific Time. NASA Television is carried on
Spacenet 2, transponder 5 (channel 9) at 69 degrees west
longitude. The frequency is 3880 MHz. Polarization is
horizontal and audio is monaural at 6.8 MHz.