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FOR IMMEDIATE RELEASESeptember 11, 2000
TROPICAL DEPRESSIONS CAN'T HIDE BEHIND CLOUDS ANYMORE
Tropical storms churning into potentially dangerous
hurricanes often hide behind a cloak of clouds. But NASA has
given forecasters a new way to peek under the covers and identify
storms much faster.
Scientists traditionally rely on satellite pictures to study
the telltale swirl of clouds of a forming storm. However, the
SeaWinds instrument aboard the QuikScat satellite can look
through the cloud cover and measure winds at the ocean's surface.
According to a new study by National Oceanic and Atmospheric
Administration (NOAA) and NASA researchers expected to be
published in a major scientific journal, SeaWinds can detect the
closed circle of winds that characterize a tropical depression up
to 46 hours sooner than conventional means.
"The SeaWinds data can help us in two ways," says paper
author Kristina Katsaros, director of NOAA's Atlantic
Oceanographic and Meteorological Laboratory, Miami, Fla. "They
can detect tropical depressions early and help us improve our
models. With more accurate information on the surface wind speed
and direction in hurricanes at all stages, our models can do a
better job of predicting a hurricane's evolution and course."
QuikScat was launched in June 1999. It travels over 90
percent of the ice-free oceans every day with a high-frequency
microwave scatterometer that provides detailed information on sea
surfaces that can be translated into wind speed and direction.
In their NASA-supported study, Katsaros and her colleagues
looked at SeaWinds data from the regions where 12 of the named
storms in the 1999 hurricane season formed. Eight of the storms
eventually developed into hurricanes. The researchers then
examined the data collected 12 to 48 hours in advance of the
storms being declared tropical depressions.
While the SeaWinds instrument wasn't always upstream of all
12 storms, it was in position to provide wind data on eight. In
those cases, it was able to detect the closed wind circulation
well before it could be seen as cloud swirls on the GOES
satellite image. The lead times ranged from three hours for
Hurricane Irene to 46 hours for Hurricane Lenny.
Being able to detect tropical depressions early is
especially important in increasing warning times in regions like
the Gulf of Mexico, where storms can grow quickly into hurricanes
and can make landfall within a few days. Early detection also may
help the National Hurricane Center plan the best use of its
resources to keep watch on developing storms.
"The ability of SeaWinds to see tropical depressions at
their earliest stage gives us the opportunity to identify and
study the elements that create hurricanes," says co-author W.
Timothy Liu, the project scientist of SeaWinds at NASA's Jet
Propulsion Laboratory (JPL), Pasadena, Calif. JPL built and
operates the QuikScat spacecraft for the Office of Earth
Sciences, NASA Headquarters, Washington, D.C.
During the current hurricane season, scientists from the
National Hurricane Center and the Hurricane Research Division are
comparing SeaWinds data with wind information from computer
models, reconnaissance aircraft, satellites, and devices that
measure temperature, moisture and relative humidity.
In a separate study, Liu combined SeaWinds data on winds
with information from another instrument, the Tropical Rain
Measuring Mission (TRMM), which can also can see through clouds
and measure rainfall in hurricanes. "Hurricanes are especially
devastating when they are accompanied by strong winds and heavy
rain," says Liu. "QuickScat and TRMM provide the only opportunity
for us to view the interplay between wind and rain before
landfall and help us to understand and predict hurricanes." The
results of this study appeared in the June 6 issue of Eos,
Transactions of the American Geophysical Union.
"This year the QuikScat data will be incorporated into a
surface-wind analysis system of NOAA's Hurricane Research
Division to produce the surface windfields in tropical storms in
near real time," says Katsaros. "This will help the National
Hurricane Center in making decisions about warning the public
when a storm threatens landfall."
QuikScat data are available from NOAA's National
Environmental Satellite and Information Service on the Internet at
Near real-time wind maps
can be viewed at http://airsea-www.jpl.nasa.gov/seaflux .
Information on NASA's Oceanography program can be found at
Managed for NASA, JPL is a division of the California
Institute of Technology in Pasadena.