Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/jplnews/1426.ZIP/1426.PR

Text File | 1993-05-03 | 6KB | 117 lines

PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE [phone]

Contact: Diane Ainsworth

FOR IMMEDIATE RELEASE                            Feb. 25, 1992


    The U.S.-French ocean topography satellite, known as the
TOPEX/Poseidon mission and scheduled for launch in mid-July, will
be able to study global weather conditions like the El Niño that
brought heavy rains to Southern California this month.
    The weather abnormality, caused by an anomalous warming of
the surface water throughout the central equatorial Pacific
Ocean, occurs about every four to seven years, usually beginning
in December.
    "The El Niño that we are having warms the Pacific Ocean
along a region of about 240 kilometers (150 miles) north and
south of the equator," said Dr. David Halpern, an oceanographer
and senior research scientist at JPL.  "El Niños typically warm
the equatorial waters by about 2 to 4 degrees Centigrade (4 to 7
degrees Fahrenheit).
    "Sometimes it produces the heavy rains, but not always," he
said.  "The last time an El Niño occurred, in 1987, it did not
influence our rains in Southern California."
    While El Niños do not always bring storm fronts to Southern
California, Halpern said, they are almost always associated with
seasons of intense rainfall.
    During a normal winter, storm patterns impacting Southern
California originate from two geographic areas.
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    "Most of the clouds in the Pacific develop in the western
tropical Pacific, where the water is generally quite warm,"
Halpern said.  "They follow a path -- known as Pineapple Alley --
from the Hawaiian Islands into Washington and Oregon."
    The other source of storms in Southern California comes from
the Gulf of Alaska and heads southward, usually veering toward
the Pacific Northwest.
    "During an El Niño, these storm patterns along Pineapple
Alley and from the Alaskan gulf are changed, moving about 1,100
to 1,600 kilometers (700 to 1,000 miles) south so that they now
fall over Southern California rather than in Oregon and
Washington," said Halpern, the first to observe the El Niño ocean
current along the equator.
    "Winds are the driving force behind ocean weather," he said.
The ocean warming in the equatorial Pacific west of the date line
is maintained by westward-blowing tradewinds.  Every several
years, the strength of these winds diminishes and sometimes
reverses direction.
    "This creates a massive flow of warm water into the central
and eastern equatorial Pacific, where the surface waters are
normally much cooler than west of the date line," he said.
    Changes in sea-surface temperature in the Pacific equatorial
waters occur at irregular intervals and in conjunction with the
"southern oscillation" -- the seesawing fluctuation of
atmospheric pressure between the eastern and the western
South Pacific.
    Because this phenomenon occurs in one of the most sparsely
populated regions of the world where very few observations aremade, it was not linked to global weather patterns, including the
United States, until quite recently.
    Oceanographers and meteorologists have traditionally relied
on National Oceanic and Atmospheric Administration (NOAA)
satellites to learn more about these ocean-atmospheric
interactions in the Pacific Ocean.
    Methods for measuring global surface winds -- a very
important dimension of sea-surface temperature fluctuations
associated with El Niños -- were introduced by an instrument
called a scatterometer on NASA-JPL's 1978 Seasat experimental
satellite.  The instrument -- which used radar to measure ocean
winds -- was "the granddaddy of a generation of scatterometers"
under development at JPL.
    The U.S.-French TOPEX/Poseidon mission will provide another
dimension to studies of ocean circulation.
    "In order to better predict El Niños, we have to understand
something about how the temperature is changed within the
interior of the ocean," Halpern said.  "The TOPEX altimeter will
allow us to measure the sea-surface height in the equatorial
Pacific, where only a few islands exist to record sea level."
    TOPEX will be able to estimate how much the water warms from
the surface to about 100 meters (328 feet) below the surface of
the ocean.  By measuring the rise of the equatorial sea surface,
scientists will know how much warm water has been introduced by
eastward-flowing currents in the upper ocean.
    Halpern, a recent visiting professor at Caltech, will be
able to improve predictions of the El Niño currents using TOPEX
data.  The surface oceanographic data from satellite radar

altimeters, scatterometers and radiometers will be assimilated
into time-dependent, three-dimensional ocean general circulation
models with advanced supercomputers to produce realistic
descriptions of the subsurface current and temperature
conditions.
    Halpern is chairman of the Pacific Ocean Panel of the
Committee on Climate Changes and the Ocean (CCCO) and a member of
the National Academy of Science's Advisory Panel on TOGA
(Tropical Ocean Global Atmosphere).  His research is conducted
for the Climate and Hydrologic System branch of NASA's Office of
Space Science and Applications.  The branch is directed by Dr.
Robert Schiffer.
    The U.S. portion of the TOPEX/Poseidon mission is managed by
JPL's Charles Yamarone, project manager, and Dr. Lee-Lueng Fu,
project scientist, for NASA's Office of Space Science and
Applications.
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