Pacific Remains Locked in Three-Year-Old Pattern: No El Nino Yet, But One Due

While change may be on the way, the Pacific is still
dominated by the strong, larger-than-El NiÒo/La NiÒa pattern
called the Pacific Decadal Oscillation (PDO), according to the
latest data from the U.S.-French TOPEX/Poseidon satellite
mission, managed by NASA’s Jet Propulsion Laboratory,
Pasadena, Calif. The PDO is a long-term ocean temperature
fluctuation of the Pacific Ocean that waxes and wanes
approximately every 10 to 20 years. “This continuing PDO
pattern of the past three years signals more of the unusually
dry conditions that have afflicted the North American west
coast,” said JPL oceanographer Dr. William Patzert.

The new satellite image, available at
http://www.jpl.nasa.gov/images/earth/pacificocean, also shows
a pulse of warm water traveling toward South America, a
reminder that another El NiÒo is due in the next year or so.
El NiÒos generally return every two to seven years; the last
one occurred in 1997. This equatorial, eastward-traveling
Kelvin wave (a bulge of warm water) is headed toward South
America at about 140 degrees West longitude. In late July,
when this wave arrives at the west coast of South America,
there should be a modest warming of the eastern Pacific.
Kelvin waves, often seen before an El NiÒo develops, are
triggered by westerly wind bursts (i.e., winds blowing in the
opposite direction from the normal easterly trade winds) in
the western Pacific. Also, the strength of El NiÒo’s next
appearance could depend on how much the PDO dominates ocean
circulation and temperature patterns over the next few years.

The data were taken during a 10-day collection cycle
ending June 11, 2001. They show that the near-equatorial ocean
has slowly warmed in the past year and sea levels and sea-
surface temperatures are near normal. 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.

In the Western Pacific, the build-up of heat, first noted
by TOPEX/Poseidon oceanographers more than two years ago, has
outlasted the La Nina of the past few years. See
http://www.jpl.nasa.gov/elnino/20000118.html . This warmth
contrasts with the Bering Sea, Gulf of Alaska and U.S. West
Coast where lower-than-normal sea surface 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.

For now, these latest TOPEX/Poseidon data show that the
entire Pacific basin continues to be dominated by the strong
and stable PDO’s characteristic warm horseshoe and cool wedge
pattern. 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 .

“Given the three-year persistence of the PDO pattern,
there will be a tendency to produce impacts similar to the
past two summers with continuing drought and heat in the
West,” said Patzert. “In some parts of the West, this long-
lasting drought has created considerable pain. In the Pacific
Northwest, water supplies are dangerously low and temperatures
should be up, which will exacerbate the energy crisis and,
like the summer of 2000, we are set up for a very busy summer
and fall fire season,” said Patzert.

“Warm oceanic patterns in the North Pacific and tropical
Atlantic suggest a more-active-than-normal hurricane season
for the U.S. East and Gulf Coasts. The only good news in this
is that the Gulf Coast and Florida could sure use the
rainfall, but the danger is that it could come as the recent
costly and painful deluge of tropical storm Allison,” said
Patzert.

The National Oceanic and Atmospheric Administration’s
(NOAA) National Weather Service U.S. winter forecast shows
little relief for drought in the West, Southeast and Florida
and a wet summer in the Midwest. NOAA seasonal forecasts can
be found at http://www.noaanews.noaa.gov/stories/s647.htm .

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. More information on TOPEX/Poseidon is available at
http://topex-www.jpl.nasa.gov .