Spaceflight Now: Breaking News

Los Ninos may be gone, but pesky Pacific pattern remains
Posted: August 30, 2000

TOPEX/Poseidon data. Photo: NASA/JPL
After three years of El Nino and La Nina with their often devastating climate consequences, the Pacific is finally calming down in the tropics but still shows signs of being abnormal elsewhere, according to the latest satellite data from the U.S.-French TOPEX/Poseidon mission.

These data, taken during a 10-day cycle of collection ending August 17, show that tropical Pacific sea levels, which indicate how much heat is stored in the ocean, have returned to near-normal (green) after three years of dramatic fluctuations.

But as summer ends in the Northern Hemisphere, remnants of the past few years remain embedded in the upper ocean. Above-normal sea surface heights and warmer ocean temperatures (indicated by the red and white areas) still blanket the far-western tropical Pacific and much of the north (and south) mid-Pacific. Red areas are about 10 centimeters (4 inches) above normal; white areas show the sea surface height is between 14 and 32 centimeters (6 to 13 inches) above normal. This contrasts with the Bering Sea and Gulf of Alaska where lower-than-normal sea levels and cool ocean temperatures continue (indicated by blue areas), although this pattern is also weakening. The blue areas are between 5 and 13 centimeters (2 and 5 inches) below normal, whereas the purple areas range from 14 to18 centimeters (6 to 7 inches) below normal.

Looking at the entire Pacific basin, the Pacific Decadal Oscillation's (PDO) characteristic warm horseshoe and cool wedge pattern is still evident in this sea-level height image. The PDO is a long-term ocean temperature fluctuation of the Pacific Ocean that waxes and wanes approximately every 10 to 20 years. Most recent National Oceanic and Atmospheric Administration (NOAA) sea-surface temperature date also clearly illustrate the persistence of this basin-wide pattern. They are available at:

"The present calming started three to four months ago when the La Nina faded away," said oceanographer Dr. William Patzert of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It appears that the global climate system is finally recovering from the past three years of dramatic swings from the extra-large El Nino of 1997/1998, which was followed by two unusually cool and persistent La Nina years."

"The good news is that we're finally out from under the El Nino and La Nina of the past three years," Patzert said. "Unfortunately, in the longer term, the reality is that the PDO pattern still dominates the Pacific and, in the short term, the atmosphere is still acting as though La Nina remains. The western United States continues hot and dry, and a larger than normal number of hurricanes are forecast by NOAA for both the Pacific and the Atlantic. Also for the remainder of the summer and into the fall, we are continuing to experience the legacy or hangover from El Nino and La Nina -- the devastating Western U.S. fires from the Canadian to Mexican borders are one example."

National Oceanic and Atmospheric Administration's (NOAA) National Weather Service has forecasted continuing heat in the Western United States and an active hurricane season for the end of summer and into the fall. NOAA seasonal forecasts can be found at:

This month marks the eighth anniversary of the launch of TOPEX/Poseidon, a mission that had been planned to last only three to five years. The satellite has orbited Earth more than 37,400 times and completed 290 10-day data collection cycles. More than 99 percent of all available mission data has been collected and archived by the operations team at JPL.

The U.S.-French TOPEX/Poseidon mission is managed by JPL for NASA's Earth Science Enterprise, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena.