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January 28, 2004
Pacific Dictates Droughts and
Drenchings
The cooler and drier conditions in Southern
California over the last few years appear to be a
direct result of a long-term ocean pattern known
as the Pacific Decadal Oscillation (PDO),
according to research presented at the 2004
meeting of the American Meteorological
Society.
The study, by Steve LaDochy, associate
professor of geography at California State
University-Los Angeles; Bill Patzert, research
oceanographer at NASA’s Jet Propulsion
Laboratory in Pasadena, Calif.; and others,
suggests Pacific oceanic and atmospheric
measurements can be used to forecast seasonal
West Coast temperatures and precipitation up to a
year in advance, from Seattle to San Diego.
An important climate controller, the PDO is a
basin-wide oceanic pattern similar to El
Niño and La Niña but much larger.
The PDO lasts many decades rather than just a few
months like El Niño and La Niña.
The climatic fingerprints of the PDO are most
visible in the North Pacific and North America,
with secondary influences coming from the
tropics. The long-term nature of the PDO makes it
useful for forecasting, as its effects persist
for so long.
Since mid-1992, NASA has been able to provide
space-based, synoptic views of the entire Pacific
Ocean’s shifts in heat content with the
Topex/Poseidon mission and its follow-up mission,
Jason (which began in 2001). Before these
satellites were available, monitoring oceanic
climate signals in near-real time was virtually
impossible.
The remarkable data and images can tag and
monitor the shifts in short-term climate events,
like El Niño and La Niña, and
long-term events such as the PDO. These data
provide a 13-year continuous, complete
time-series of two major El Niños and two
La Niñas, and have made it possible to
detect a major phase shift of the PDO. Patzert
and LaDochy show these data, combined with
longer-term studies of land-based data, provide a
powerful set of forecasting tools.
The PDO shifted to a negative, cool phase,
leading to wetter conditions in the U.S. Pacific
Northwest, and drier than normal conditions in
Central and Southern California this decade.
Since the last 1997-1998 El Niño, the Los
Angeles area had only 79 percent of its normal
rainfall, Patzert said. Lake Mead, the great
fresh-water reservoir in southeast Nevada, is at
less than 50 percent of normal capacity. Also,
huge West Coast fires over the past few years
have been greatly exacerbated by PDO-induced
drought, Patzert added.
“These shifts in the PDO are long-term
tendencies, which actually have a bigger economic
impact than El Niño,” said Patzert.
“People talk about floods from El
Niño, but what really has a harsh and
costly impact is a five-year drought.”
“A full cycle of the PDO (cool to warm
and back to cool) runs about 50 years,”
said LaDochy. “Over the next several years
there is going to be a tendency toward dry and
colder temperatures in the southern U.S. West
Coast. It is very difficult to forecast
day-to-day here on the West Coast, but we can say
with some confidence that over the next five
years, we’d better start saving
water.”
The researchers used over 50 years of U.S.
climatic information, and Pacific atmospheric and
oceanic data from the National Oceanic and
Atmospheric Administration National Centers for
Environmental Prediction. By comparing data sets,
they saw strong correlations between Pacific
climate patterns, temperatures and precipitation
trends on the West Coast. They then were able to
develop “hindcasts” to explain
temperature and precipitation variability for
West Coast regions. These decadal cycles also
will be useful for explaining future regional
climate variability.
NASA’s Earth Science Enterprise is
dedicated to understanding the Earth as an
integrated system and applying Earth System
Science to improve prediction of climate, weather
and natural hazards using the unique vantage
point of space.
For more information and images about the
research on the Internet, visit:
http://www.gsfc.nasa.gov/topstory/2004/ 0116westcoast.html
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Contacts:
Elvia H. Thompson
Headquarters,
Washington
(Phone: 202/358-1696)
Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-0474)
Krishna Ramanujan
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 607/273-2561)
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Pacific Decadal Oscillation, January 8,
2000
This image shows a horseshoe of higher than
average (warm) water in western and central
Pacific Ocean (red and white), and lower than
average (cool) blue and purple water in the
eastern and tropical Pacific Ocean. This leads
scientists to believe we entered the cool phase
of the PDO over 1997. Credit: NASA
High-Resolution
Image
Positive and Negative Phases of Pacific
Decadal Oscillation
This image shows the Pacific Ocean sea surface
temperature changes associated with positive and
negative phases of the Pacific Decadal
Oscillation. The colors in these maps represent
temperature anomalies—differences from the
average sea surface temperature during the cool
and warm phases of the PDO. Units are degrees
Celsius. Credit: Image courtesy of Steven Hare
and Nathan Mantua, University of Washington.
Jason-1 Image of Pacific Ocean, January
23, 2004
The latest remote sensing data from
NASA’s Jason satellite show that the
equatorial Pacific sea surface levels are higher,
indicating warmer sea surface temperatures in the
central and west Pacific Ocean. This pattern has
the appearance of La Niña rather than El
Niño. This 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
and purple areas). Although subtle, the negative
PDO anomaly pattern can be seen in this early
2004 image.
The image above is a global map of sea surface
height, accurate to within 30 millimeters. The
image represents data collected and composited
over a 10-day period, ending on Jan 23, 2004. The
height of the water relates to the temperature of
the water. As the ocean warms, its level rises;
and as it cools, its level falls. Yellow and red
areas indicate where the waters are relatively
warmer and have expanded above sea level, green
indicates near normal sea level, and blue and
purple areas show where the waters are relatively
colder and the surface is lower than sea level.
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. Credit: NASA
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