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.
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 NASAs 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
The study, by Steve LaDochy, associate professor of geography at California State University-Los Angeles; Bill Patzert, research oceanographer at NASAs 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.
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