PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011

PHOTO CAPTION                                         P-45140
                                             January 24, 1995

These three panels show the evolution of  sea surface elevation 
over the global oceans from October to December 1994.  The 
red-colored strips in the central and eastern tropical Pacific 
reflect the formation of the present El Nino condition. The 
images were created with the sea surface elevation data taken by 
the radar altimeter onboard the TOPEX/Poseidon satellite.  The 
color coded maps show monthly  sea surface elevation relative to 
the two-year average taken during 1993-94.  Higher sea surface 
elevation is shown in red and yellow while lower elevation
is in purple and blue.  The higher sea surface elevation 
associated with the El Nino reflects an excessive amount of 
unusually warm water in the upper ocean.  El Nino begins when a 
phenomenon called a Kelvin wave is created in the western 
tropical Pacific when the trade winds weaken.  The Kelvin wave 
subsequently travels eastward along the equator carrying with it 
an unusually warm water mass under a bulge of high sea surface 
elevation. These maps show a new Kelvin wave arriving at the 
western coast of South America in November 1994.  In December, 
scientists believe the trailing part of the wave was somehow 
reinforced, causing the wave to stagnate in its present location. 
 The red and white feature shown in the Indian Ocean is caused by 
seasonal monsoon winds.  TOPEX/Poseidon is a joint program of 
NASA and the Centre Nationale d'Etudes Spatiales, the French 
space agency. Scientists use the TOPEX/Poseidon sea surface 
elevation data to produce global maps of ocean circulation.  
Launched Aug. 10, 1992, the satellite has completed two and a 
half years of its three-year prime mission and has provided 
oceanographers with unprecedented global sea surface elevation 
that is accurate to better than 5 centimeters (2 inches).  The 
Jet Propulsion Laboratory manages the TOPEX/Poseidon satellite 
for NASA's Office of Mission to Planet Earth.

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