El Nino is a climatic event that can bring devastating weather to several parts of the world, including the recent heavy rains and flooding in California, and the warmer than normal winter in the eastern United States.
"The satellite has observed high sea-surface elevation, which reflects an excessive amount of unusually warm water in the upper ocean," said Dr. Lee-Lveng Fu, JPL Topex project scientist at NASA's Jet Propulsion Laboratory, Pasadena, CA. "The associated excess of heat creates high sea-surface temperatures, which affect the weather worldwide by heating the atmosphere and altering the atmospheric jet streams."
Jet streams are high-level winds, five to ten miles above the Earth's surface, created when warm and cold air masses meet. Shifts in the location of jet streams change temperatures and precipitation zones at the surface.
El Nino begins when the westward trade winds weaken and a large warm water mass, called a Kelvin wave, is allowed to move eastward along the equator in the Pacific Ocean. Data from the radar altimeter onboard Topex, recorded from October through December 1994, reveal a new Kelvin wave moving toward the western coast of South America.
"This wave is currently occupying most of the tropical Pacific Ocean. It will take another month or two before the wave disperses. Compared to the El Nino condition of the winter of 1992-93, the present one appears somewhat stronger and might have stronger and longer lasting effects," Fu said.
Topex, a joint program of NASA and the Centre Nationale d'Etudes Spatiales, the French space agency, uses a radar altimeter to precisely measure sea-surface height. Scientists use the Topex 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 level measurements that are accurate to better than 2 inches (5 centimeters).
"The global sea-surface elevation information provided by Topex is unique because it is related to the amount of heat stored in the upper ocean, which is important for long-range weather forecasting. The speed and direction of ocean currents also can be determined from the elevation information, providing another piece of critical information about the ocean, which is the key to climate change," Fu continued.
Topex is part of NASA's Mission to Planet Earth, a coordinated, long-term research program to study the Earth's global environment. Topex will provide the first comprehensive, consistent measurements of the circulations of the ocean.