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Pacific Dictates Droughts And Drenchings

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  • npat1@juno.com
    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
    Message 1 of 1 , Feb 4, 2004
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      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
      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

      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

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