Topex/Poseidon data

More than a decade after affecting climate on a global scale, residual signs of a powerful El Nio are still visible from space.

Oceanographers using data from the U.S.-French TOPEX/Poseidon satellite are tracking the remnant wave of the 1982-83 El Nio event as it moves across the Northwest Pacific Ocean, where some scientists theorize it may still be affecting weather in the region.

El Nio is a climatic phenomenon that can bring devastating weather to several global regions, including heavy rains and flooding to California, colder than normal winters across the United States and severe droughts and dust storms to Australia.

"The fact that we are seeing this wave 10 years later is an amazing discovery in and of itself," said Dr. Gregg Jacobs of the Naval Research Laboratory (NRL) facility located at the Stennis Space Center, Mississippi. "The ability to observe changes in global ocean circulation as we have seen over the Kuroshio region is a demonstration that the TOPEX/Poseidon satellite is the most valuable global ocean observing tool we have. We wouldn't have been able to do this work without TOPEX/Poseidon," Jacobs continued.

An El Nio begins when warm water builds up in the equatorial Pacific and moves eastward toward the coast of the Americas. When this movement, called a Kelvin wave, reaches the coastline, it is "reflected" and moves back across the Pacific in the form of a Rossby wave that continues to affect climate and ocean circulation. The 1982-83 El Nio was the worst such event this century, and its effects were felt around the world.

NRL oceanographers noticed the Rossby wave produced by the 1982-83 El Nio while they were studying TOPEX/Poseidon ocean-circulation data of the Kuroshio current off the coast of Japan.

"The TOPEX/Poseidon data showed the Kuroshio current farther north than it has been observed in earlier data sets," said Jacobs. "While we were investigating this intriguing change, we discovered the Rossby wave was actually pushing the current northward, raising the temperature of the northwest Pacific."

TOPEX/Poseidon, 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/Poseidon data to produce global maps of ocean circulation, which can be used to identify Kelvin and Rossby waves.

The Jet Propulsion Laboratory manages the U.S. portion of the TOPEX/Poseidon mission for NASA.

TOPEX/Poseidon is part of NASA's Mission to Planet Earth, a coordinated, long-term research program to study the Earth as a single global environment. TOPEX/Poseidon's sea- surface height data are essential to understanding the role oceans play in regulating global climate, one of the least understood areas of climate research.

The TOPEX/Poseidon data will enable oceanographers to monitor the movement of other Rossby waves initiated by El Nio events during the past decade. The El Nios of 1986-87 and 1991-93 have produced Rossby waves that are now propagating across the Pacific Ocean. With continued observations from TOPEX/Poseidon, oceanographers will be able to study the development and impact of these waves.

"As we now know, these waves are capable of producing dramatic changes in climate, and TOPEX/Poseidon provides the key to watching for these changes and allowing us to prepare for them," Jacobs said.

While oceanographers still can't predict exactly when an El Nio event will occur, the TOPEX/Poseidon data do give them several months warning before the onset of a new event.

"And unlike El Nio events, Rossby waves are much more predictable," according to Jacobs. "Given the year of an El Nio, we know exactly when the Rossby wave's effects will be felt on the opposite side of the Pacific Ocean.

"As the world's population grows, humanity becomes more dependent upon reliable resources. Interruptions such as El Nio are made more devastating by their sudden, unforeseen appearance. The monitoring and understanding of the world's oceans provided by TOPEX/Poseidon helps mitigate the possible disastrous consequences of what is Earth's nature cycle."

Launched Aug. 10, 1992, the satellite has completed two years of its three-year prime mission and has provided oceanographers with unprecedented global sea level measurements that are accurate to less than 5 centimeters (2 inches).

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