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Strong, long-lasting La Niña just fading away
June 19, 2000
After dominating the tropical Pacific Ocean for more than
two years, the 1998-2000 La Nina "cool pool" is continuing its
slow fade and seems to be retiring from the climate stage,
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
June 9, show that the equatorial Pacific continues to warm up and
is returning to normal (green) as this latest, persistent, two-
year La Nina episode is coming to an end. Only a few patches of
cooler, lower sea levels (seen in blue and purple) remain across
the tropics. It should be noted that in June 1999, La Nina barely
had a pulse, but was resuscitated in fall 1999. (See the
June 29,1999 press release on that topic.)
The blue areas are between 5 and 13 centimeters (2 and 5
inches) below normal, whereas the purple areas range from 14 to
18 centimeters (6 to 7 inches) below normal. In the far-western
tropical Pacific Ocean, the ocean remains higher and warmer than
normal. In summary, it appears that the global climate system is
finally emerging 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, according to
scientists at NASA's Jet Propulsion Laboratory.
But as the northern hemisphere summer begins, above-normal
sea surface heights and warmer ocean temperatures (indicated by
the red and white areas) still blanket the western equatorial
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 region southward along the western coast of
North America, where lower-than-normal sea levels and cool ocean
temperatures continue, although this pattern is also weakening.
A possible switch in this larger-than-El Nino/La Nina, slower-
changing pattern -- the Pacific Decadal Oscillation -- was first
noticed by many scientists in late 1998. See the
January 18, 2000 press release on that
topic, or for further
information and graphics about the Pacific
Decadal Oscillation.
"Let's not forget that the legacy of two years of La Nina
will be with us this summer and into the fall, " said JPL
oceanographer Dr. William Patzert. "Much of the nation's
farmland is really dry in many regions. The reality is that the
atmosphere is still acting as though La Nina remains." The
National Oceanic and Atmospheric Administration's (NOAA) National
Weather Service has forecasted continuing drought for much of the
midwestern and southeastern United States and an active hurricane
season for our coming summer. NOAA seasonal forecasts can be
found at http://www.cpc.ncep.noaa.gov .
The U.S.-French TOPEX/Poseidon mission is managed by JPL for
the 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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