Pacific Dictates Droughts And Drenchings
- Forward from SpaceDaily
Greenbelt - Feb 04, 2004
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 Ni�o and La Ni�a but much larger. The PDO lasts many
decades rather than just a few months like El Ni�o and La Ni�a. 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 Ni�o and La Ni�a, and long-term events
such as the PDO. These data provide a 13-year continuous, complete
time-series of two major El Ni�os and two La Ni�as, 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
Nino, 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 Ni�o," said Patzert. "People talk about
floods from El Ni�o, but what really has a harsh and costly impact is a
"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
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.
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
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
Only $14.95/ month - visit www.juno.com to sign up today!