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Contact: Mary Hardin
     
EMBARGOED FOR RELEASE 9 A.M. PACIFIC TIME DEC. 7, 1994

     Scientists using data from the U.S.-French oceanography 
satellite TOPEX/Poseidon say they appear to have detected a 
rise in the average global sea level over the past two 
years.  This and several other findings were announced today 
at the American Geophysical Union's fall meeting in San 
Francisco.

     Other topics at the meeting related to TOPEX/POSEIDON 
include an experiment to study phenomena that can disrupt 
offshore drilling and studying deep-ocean tides.

     If scientists detect a global, long-term rise in sea 
level, they will be able to test theories about the effects 
of climate change.

     "A rise in global mean sea level is an important 
indicator of global change, because it can be caused by 
thermal expansion of the oceans and melting of glaciers and 
the polar ice caps," said Dr. R. Steven Nerem, of  NASA's 
Goddard Space Flight Center, Greenbelt, Md.  "Therefore, if 
a long-term rise in global mean sea level were detected, 
this would provide further evidence to support the global 
warming predicted by some climate models due to an increase 
in the 'greenhouse' gases.

     "The data (from December 1992 to September 1994) show a 
rise in average sea level of about 3 millimeters (0.12 
inches) per year, which is in reasonable agreement with the 
tide gauge results," Nerem explained.

     Data collected from tide gauges over the last century 
suggest that average sea level has been rising at a rate of 
about 1 to 2 millimeters (0.04 to 0.08 inches) per year, 
roughly equivalent to the rate expected from global warming, 
Nerem said.  However, tide-gauge measurements can be 
affected by the movement of land masses and are too sparsely 
distributed to provide global coverage.

     TOPEX/Poseidon was launched on Aug. 10, 1992 to study 
how long-term ocean circulation affects climate change.  
TOPEX/Poseidon measures the sea-surface height along a 
groundtrack that repeats once every 10 days.  The satellite 
measures absolute sea level relative to the center-of-mass 
of the Earth, and the data is unaffected by land movements.

     Nerem cautioned that the results are preliminary and 
could change as a longer time series is collected and as the 
measurement errors are better understood. 

     "It should also be noted that since the sea level rise 
is only measured over two years, it could represent a short-
term variation unrelated to the long-term signal expected 
from global warming.  Nevertheless, TOPEX/Poseidon appears 
to be providing corroborating evidence that global sea level 
is indeed rising," Nerem said.

     In the Gulf of Mexico, TOPEX/Poseidon data are helping 
scientists and a U.S. oil company study potentially 
dangerous ocean phenomena that can disrupt off-shore oil 
drilling.

     "Oil industry operations in deep water can be adversely 
affected by high ocean currents," said Dr. George Born, of 
the University of Colorado's Colorado Center for 
Astrodynamics Research (CCAR).  "In the gulf, eddies spun 
off from the Loop Current have caused serious operational 
problems, including delays of several weeks, lost and 
damaged equipment and millions of dollars in unproductive 
expense." 

     The Loop Current is a strong ocean current that 
circulates around the Gulf of Mexico.  Roughly once a year, 
a large eddy is spun off from the Loop Current and moves 
west through the gulf.

     "An eddy can be thought of as a hurricane in the 
water," Born said.  "The Gulf of Mexico has some of the 
largest eddies in the world, ranging up to 300 to 400 
kilometers (180 to 250 miles) in diameter."

     In late summer 1994, a large eddy, called Eddy Yucatan, 
broke off from the Loop Current.  Oceanographers from Texaco 
Inc. used TOPEX/Poseidon data to augment their drifting buoy 
data and track this eddy.  As of late October, the center of  
Eddy Yucatan  was located approximately 150 kilometers (93 
miles) southeast of the Texaco drilling site and it appeared 
to be moving away from the site.

     "However, the predictive models available for the gulf 
are still under development and it is impossible to predict 
the future path of the eddy with great certainty," Born 
said.  "Work is currently under way to use TOPEX/Poseidon 
data to produce a more reliable forecast.  This work 
ultimately will benefit not only off-shore oil drilling, but 
many oceanographic activities in the Gulf of Mexico."

     In another application, the precision of the 
TOPEX/Poseidon ocean measurements has enabled scientists to 
calculate global tides across all the open oceans, an 
important step toward monitoring global ocean circulation 
from space and understanding the complexities of global 
climate change.

     "Using the first year of data we can now predict deep 
ocean tides everywhere over the areas covered by the 
satellite with an accuracy of 2 to 3 centimeters (0.8 to 1.1 
inches)," said Dr. Christian Le Provost, of the National 
Scientific Research Center in France. 

     "We need to precisely understand deep ocean tides so 
that we can remove their influence from the ocean 
circulation data," said Dr. Lee-Lueng Fu, the TOPEX/Poseidon 
project scientist at NASA's Jet Propulsion Laboratory, 
Pasadena, Calif.  "It is ocean circulation that is the key 
to understanding global warming and global climate change." 

     Precise knowledge of global ocean tides helps 
scientists better understand how pollutants are dispersed by 
tidal currents.  The information also has applications for 
shipping, oil drilling and exploration, and fishery 
development. 

     TOPEX/Poseidon is part of NASA's Mission to Planet 
Earth, a coordinated, long-term research program to study 
the Earth as a single global environment.  TOPEX/Poseidon's 
sea-surface height data are essential to understanding the 
role oceans play in regulating global climate, one of the 
least understood areas of climate research.  The Jet 
Propulsion Laboratory manages the TOPEX/Poseidon mission for 
NASA.

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MAH 11/30/94
#9469

NOTE TO EDITORS:  The TOPEX/Poseidon press conference is 
scheduled for 9 a.m. Wednesday, Dec. 7 in Room 111 of  San 
Francisco's Moscone Center.  The science team members cited 
in the release can be contacted through the AGU newsroom at 
(415) 905-1807.