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Tech

El Niņo spurs rise in global average sea level

December 9, 1998
Web posted at: 3:20 PM EST

By Environmental News Network staff

A key to understanding the changes in the ocean are the global maps made by TOPEX/Poseidon satellite. The sea level rise was not confined to the tropical Pacific, but also was observed in the Indian Ocean and the southern Pacific.
A key to understanding the changes in the ocean are the global maps made by TOPEX/Poseidon satellite. The sea level rise was not confined to the tropical Pacific, but also was observed in the Indian Ocean and the southern Pacific.
(ENN) -- Average global sea level rose by about 2 centimeters (0.8 inch) during the 1997-98 El Niņo event and has now returned to normal levels, according to scientists studying TOPEX/Poseidon satellite measurements of sea surface height.

This is the first time scientists have been able to link El Niņo to a change in average global sea level, said Dr. R. Steven Nerem, a TOPEX/Poseidon science team member at the Center for Space Research at the University of Texas at Austin.

"Understanding these short-term variations is important for understanding and detecting long-term variations caused by climate change," he said.

The satellite measures global sea level at 10-day intervals with a precision of 0.4 centimeters (0.16 inches), making the 2 centimeter (0.8 inch) change relatively easy, said Nerem.

"However, these results tell us that detecting sea level variations caused by climate change will be more difficult because such changes are significantly smaller than the variations we have observed during the El Niņo."

Global mean sea level change on seasonal and inter-annual time scales is a measure of the changing heat content of the ocean. The 2-centimeter (0.8-inch) rise during the El Niņo implies that, on average, the global ocean may be gaining heat.

"Average global sea level began rising in late March 1997, peaked at 2 centimeters (0.8 inches) above normal in early November 1997, and then began falling back to normal by the end of July 1998. Sea surface temperature changes began rising in late October 1996, peaked at 0.4 degrees Celsius (0.7 degrees Fahrenheit) in late December 1997, and fell back to 0.1 C (0.2 F) at present," said Nerem.

The TOPEX/Poseidon satellite, launched in August 1992, uses an altimeter to bounce radar signals off the ocean's surface to get precise measurements of the distance between the satellite and the sea surface. These data are combined with measurements from other instruments that pinpoint the satellite's exact location in space.

Every 10 days, scientists produce a complete map of global ocean topography, the barely perceptible hills and valleys found on the sea surface. A follow-on mission to TOPEX/Poseidon, Jason-1, is scheduled for launch in 2000.

Copyright 1998, Environmental News Network, All Rights Reserved


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