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Pacific may repel El Niños but not other climate woes
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 years," said Dr. William Patzert of NASA's Jet
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.
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