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May 17, 2007 "With this
technique,
meteorologists for the first time will be able to monitor the strength
of a
hurricane every few minutes as it approaches landfall and quickly alert
coastal
communities if it suddenly intensifies or weakens," says NCAR scientist
Wen-Chau Lee. The technique is
known as
VORTRAC, which stands for Vortex Objective Radar Tracking and
Circulation. VORTRAC uses the
Doppler radar
network established by the National Oceanic and Atmospheric
Administration
(NOAA) in the 1980s and 1990s. About 20 of these radars are scattered
along the
Gulf and Atlantic coastlines from Lee and his
collaborators
developed a series of mathematical formulas that combine data from a
single
radar near the center of a landfalling storm with general knowledge of
Atlantic
hurricane structure in order to map the approaching system's winds in
three
dimensions. The technique also infers the barometric pressure in the
eye of the
hurricane, a very reliable index of its strength. Forecasters using
VORTRAC can
update information about a hurricane each time a NOAA Doppler radar
scans the
storm, which can be as often as about every six minutes. Without such a
technique, forecasters would need at least two coastal radars in close
proximity to each other in order to obtain the same information. But
most of
the network's radars are too far apart to qualify. Because of the
limited range of
Doppler radars, VORTRAC works only for hurricanes that are within about
120
miles of land. Depending on a hurricane's speed, that could enable
forecasters
to monitor it for the critical 10-15 hours or so before landfall. The To monitor the winds
of a
landfalling hurricane, forecasters now rely on aircraft to drop
instrument
packages into the storm that gather data on winds and pressure. But due
to
flight logistics, the aircraft can take readings no more than every few
hours,
which means that coastal communities may not be swiftly alerted to
changes in
approaching hurricanes. In 2004, parts of Lee and his
collaborators applied
VORTRAC retroactively to Hurricane Charley. In a recent article in
Geophysical
Research Letters, they reported that the technique would have
accurately
captured the burst in the hurricane's intensity. "Our research shows
that
this technique can capture sudden intensity changes in potentially
dangerous
hurricanes," says NCAR scientist Michael Bell, a coauthor of the
article. In time, VORTRAC may
also help
improve long-range hurricane forecasts by using data from airborne
radars to
produce detailed information about a hurricane that is far out to sea.
Forecasters could input the data to computer models to improve three-
and
five-day forecasts. The research was
funded primarily
by the National Science Foundation and NOAA.
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