|
September 6, 2007
NEW FARAWAY SENSORS WARN OF
EMERGING
HURRICANE'S STRENGTH
Days before a growing hurricane possibly
batters a local
coastline, meteorologists rush to predict just how strong its winds and
rains
may grow knowing that lives and an area’s economy may depend
on their results.
A new study supported by NASA and the U.S. Office of Naval Research
takes
forecasters one step further to improving their ability to predict just
how
powerful an oncoming storm may become by using highly-sensitive sensors
located
thousands of miles from the storm to detect lightning outbreaks within
a
hurricane’s most dangerous area.
Researchers can now investigate with greater accuracy how the rate of
lightning
strikes produced within a hurricane's eyewall is tied to the changing
strength
of that hurricane. A hurricane’s eyewall is the inner
heat-driven region of the
storm that surrounds the “eye” where the most
intense rainfall and most
powerful winds occur. By monitoring the intensity of lightning near a
hurricane’s eye, scientists will be able to improve their
forecasts of when a
storm will unleash its harshest conditions.
During the study, researchers used data from a growing network of new,
long-range, ground-based lightning sensors, a NASA satellite and
aircraft-based
sensors. They explored the relationship between eyewall lightning
outbreaks and
the intensity of two of the most severe Atlantic storms on record
before they
made U.S.
landfall: category five hurricanes Katrina and Rita. An article on this
research, also supported by the U.S. Office of Naval Research, will be
published in the American Meteorological Society's Monthly Weather
Review later
this year.
"There are very few observing systems that offer a broad view of a
storm
over the open ocean where hurricanes tend to build or lose strength,"
said
lead author Kirt Squires, a recent graduate of the meteorology program
at the University
of Hawaii
in Honolulu.
"What’s really compelling about the new sensors is their
increased
sensitivity to pick up lightning's electromagnetic signal over water
from such
a long distance. As a result, we can see thunderstorm activity over the
ocean
from thousands of miles away for the first time. This development is
essential
to improving the way meteorologists can look at a growing storm to
judge just
how harsh it will be."
When water condenses from vapor into a cloud droplet, latent or hidden
heat is
released, which in turn builds updrafts – air moving upwards
in a cloud. Latent
heat provides the energy that fuels hurricanes. If the ensuing updrafts
are
strong enough, they can cause the separation of charge that produces
lightning.
The tight correlation between the rate of lightning strikes, the amount
of
rainfall and the heat released in the eyewall of a storm allows the
lightning
rate data to be useful in computer models that forecast hurricane track
and
intensity.
"Hurricane forecasters and researchers are very interested in
developing
methods that allow a continuous examination of the structural growth of
the
eyewall within hurricanes," said co-author Steven Businger, a senior
professor of meteorology at the University of Hawaii.
"The fact
that lightning is directly linked to the heat energy released in the
eyewall
makes it a priority for us to examine the evolution of lightning within
a
storm."
Researchers studied data on intensity and lightning strike rate from
hurricanes
Katrina and Rita, both from 2005. They were trying to determine whether
a link
existed between the two traits. The researchers combined data from
NASA's
Tropical Rainfall Measuring Mission satellite's microwave radiometers
and from
sensors onboard the National Oceanic and Atmospheric
Administration’s P-3
“hurricane hunter” aircraft that fly into the
storm, with the enhanced sensor
capability of the NASA co-funded Pacific Lightning Detection Network.
The network comprises four state-of-the-art, long-range,
high-sensitivity
sensors located around the central northern Pacific
Ocean.
Businger is working with the U.S.
division of Finnish technology firm Vaisala, Tucson, Ariz.,
and other agencies to expand the network with eight additional sensor
sites by
the end of 2008. It is part of the larger North American Lightning
Detection
Network of nearly 200 sensors that monitors lightning over the Gulf of
Mexico
and the Atlantic
and Pacific oceans.
Though Businger acknowledges that more research is needed, results from
this
study show that the growth and density of lightning strikes in a
hurricane's
eyewall provide important insight into the inner workings of the most
powerful
storms on Earth, information that may in the future help save lives
through
improved hurricane forecasts.
Writer:
Gretchen
Cook-Anderson
Goddard Space Flight Center
For more information, visit:
http://www.nasa.gov/mission_pages/hurricanes/main/index.html
##
Contact:
Laura
Spector
Goddard
Space Flight Center
301-286-0918
laura.a.spector@nasa.gov
This text is derived from:
http://www.nasa.gov/centers/goddard/news/topstory/2007/lightning_hurricane.html
Recommend this Article to a Friend
Back to: News |