JPL Satellite Detects Drop in Sea Levels

A U.S.-French satellite showed that sea levels dropped 12 inches off the East Coast last winter as cold air chilled the Atlantic Ocean and made the water contract.

The Topex-Poseidon satellite also found that during the same period, from October, 1992, to March, 1993, sea levels rose 12 inches in parts of the Southern Hemisphere, where warm summer air heated the oceans and made the water expand.

The measurements are the most accurate yet of global sea level changes, and show how sea levels are affected by winds and seasonal temperature changes in ocean water, said Lee Fu, chief scientist of the $706-million project at the Jet Propulsion Laboratory.

Topex-Poseidon bounces radar beams off the world’s oceans to measure sea levels and calculate wind speeds and ocean currents. Scientists are using that information to learn more about how the oceans circulate and to improve their ability to predict weather, climate disruptions and the severity of global warming from industrial pollution.

By removing the effects of tides, scientists can use Topex-Poseidon’s measurements to learn how seasons, winds and other factors affect sea levels.

Cold continental air masses blowing off North America and Asia were responsible for the 12-inch wintertime drop in sea levels detected off the East Coast in the Atlantic Ocean’s Gulf Stream and off the east side of Japan, the National Aeronautics and Space Administration said.

Topex-Poseidon also detected a seasonal drop in sea level at the Equator in the Pacific and Atlantic oceans, due mainly to seasonal changes in trade winds.

In a similar manner, seasonal monsoon winds caused sea levels to drop in the eastern and southern Indian Ocean and rise in the northwestern part of that ocean, NASA said.

Topex-Poseidon is the first major space mission conducted jointly by the United States and France.