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Pacific may repel El Niños but not other climate woes
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January 29, 2001

The El Niño and La Niña events of the past few years may have faded into climate history, but the Pacific Ocean has not calmed down. The latest satellite data from the U.S.-French TOPEX/Poseidon mission show that the entire Pacific basin continues to be dominated by the strong and stable Pacific Decadal Oscillation's (PDO) characteristic warm horseshoe and cool wedge pattern. The PDO is a long-term ocean temperature fluctuation of the Pacific Ocean that waxes and wanes approximately every 10 to 20 years.

"While this PDO pattern tends to make the formation of a new El Niño event less likely, it may signal a continuation of the unusually dry conditions that have afflicted the West Coast in the past two Propulsion Laboratory in Pasadena, Calif.

These data, taken during a 10-day collection cycle ending January 3, 2001, show that 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. See the El Niño/La Niña Watch page. 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 build-up of heat dominating the Western Pacific was first noted by TOPEX/Poseidon oceanographers more than two years ago and has outlasted the El Niño and La Niña events of the past few years. See January 27, 1999. This warmth contrasts with the Bering Sea, Gulf of Alaska and tropical Pacific where lower-than-normal sea levels and cool ocean temperatures continue (indicated by blue areas). 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. Actually, the near-equatorial ocean cooled through the fall and into the early winter and is now almost La Niña-like.

Looking at the entire Pacific basin, the Pacific Decadal Oscillation's warm horseshoe and cool wedge pattern still dominates this sea-level height image. Most recent National Oceanic and Atmospheric Administration (NOAA) sea-surface temperature data also clearly illustrate the persistence of this basin-wide pattern. They are available at http://psbsgi1.nesdis.noaa.gov:8080/PSB/EPS/SST/climo.html .

What does all this mean for seasonal climate forecasters? Less is understood about forecasting climate over North America based only on the phase of the PDO than on an El Niño or La Niña. But, Patzert said, "The present 'cool' or 'negative' phase of the PDO looks a lot like and tends to produce impacts similar to the La Niña of the past two winters and springs. The big debate among climate scientists is whether we are entering a long-lasting negative PDO episode," said Patzert.

"If yes, the next few years could be 'forward to the past,' resembling the dry years of the early to mid-1950s and the late 1980s when many regions of the United States experienced sustained and painful drought. Rainfall was as much as 20 to 40 percent below normal. We could be seeing those kind of conditions again."

"The good news is that as long as the present Pacific pattern hangs in there, it will act as a strong El Niño repellent. From knowledge of past climate, we know that the negative phases of the PDO tend to discourage large El Niños. Thus, looking ahead for the next few years, there is a low probability of a repeat of the Super El Niño of 1997 to 1998," Patzert said.

The National Oceanic and Atmospheric Administration's (NOAA) National Weather Service U.S. winter forecast suggests enhanced possibility for heavy rain events from Northern California to southern Alaska, cold air outbreaks and Great Lakes snow events, and more freeze events along the East Coast and in the Southeast. NOAA seasonal forecasts can be found at http://www.cpc.ncep.noaa.gov/products/winter_outlook/ .

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. For more information on the TOPEX/Poseidon project, see: http://topex-www.jpl.nasa.gov.


Source: Jet Propulsion Laboratory

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