Artist concept of Jason

During the first six months of their mission, scientists using the U.S.-French TOPEX/Poseidon oceanographic satellite have recorded the most accurate measurements to date of global sea level changes.

The data will be used by oceanographers to calibrate the computer models which help forecast future climate changes.

"The changes in sea level we have observed during the first six months from October 1992 to March 1993 are a combination of the effects of seasonal warming and cooling as well as wind," said Lee-Lueng Fu, TOPEX/Poseidon project scientist at NASA's Jet Propulsion Laboratory.

In the Northern Hemisphere, the sea level in the Gulf Stream off the United States east coast and the sea level in the Kuroshio regions east of Japan dropped by more than 30 centimeters (12 inches). Most of this drop was caused by the winter cooling of the ocean by the cold continental air mass blown off the North American and Asian continents, Fu said.

In the Southern Hemisphere, a corresponding sea level rise occurred at similar latitudes which resulted from the warming of the summer atmosphere.

"It takes an increase or decrease of 1 degree Celsius in the average temperature of a water column of 50 meters deep to cause the sea level to rise or fall by 1 centimeter," Fu explained.

The sea level change in the Northern Hemisphere is larger than that in the Southern Hemisphere because the larger land mass of the Northern Hemisphere creates a colder continental air mass that cools the ocean water off the east coasts of North America and Asia.

Seasonal changes in the trade winds caused a drop in sea level at the equator in both the Pacific and Atlantic oceans, Fu said. The rise in sea level in the eastern tropical Pacific Ocean off the coast of South America was the remnant of the Kelvin wave pulses that began in December 1992. A Kelvin wave pulse creates a surge of warm water that moves eastward along the equator and can contribute to El Ni┬Ło conditions.

In the Indian Ocean, seasonal monsoon winds caused a fall in sea level in the eastern and southern regions and a rise in sea level in the northwestern region.

JPL manages the NASA portion of the joint U.S.-French mission for NASA's Office of Mission to Planet Earth. Launched Aug. 10, 1992, the satellite is part of NASA's long-term effort to study Earth as a global environmental system.

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