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January 12, 2004
A “Hot Tower” Above The Eye
Can Make Hurricanes Stronger
They are called hurricanes in the Atlantic,
typhoons in the West Pacific, and tropical
cyclones worldwide; but wherever these storms
roam, the forces that determine their severity
now are a little less mysterious. NASA
scientists, using data from the Tropical Rainfall
Measuring Mission (TRMM) satellite, have found
“hot tower” clouds are associated
with tropical cyclone intensification.
Owen Kelley and John Stout of NASA’s
Goddard Space Flight Center, Greenbelt, Md., and
George Mason University will present their
findings at the American Meteorological Society
annual meeting in Seattle on Monday, January
12.
Kelley and Stout define a “hot
tower” as a rain cloud that reaches at
least to the top of the troposphere, the lowest
layer of the atmosphere. It extends approximately
nine miles (14.5 km) high in the tropics. These
towers are called “hot” because they
rise to such altitude due to the large amount of
latent heat.Water vapor releases this latent heat
as it condenses into liquid.
A particularly tall hot tower rose above
Hurricane Bonnie in August 1998, as the storm
intensified a few days before striking North
Carolina. Bonnie caused more than $1 billion
damage and three deaths, according to the
National Oceanic and Atmospheric Administration
National Hurricane Center.
Kelley said, “The motivation for this
new research is that it is not enough to predict
the birth of a tropical cyclone. We also want to
improve our ability to predict the intensity of
the storm and the damage it would cause if it
struck the coast.” The pioneering work of
Joanne Simpson, Jeffrey Halverson and others has
already shown hot towers increase the chance a
new tropical cyclone will form. Future work may
use this association to improve forecasts of a
cyclone’s destructive potential.
To achieve their goal, Kelley and Stout needed
to compile a special kind of global statistics on
the occurrence of hot towers inside tropical
cyclones. The only possible data source was TRMM
satellite, a joint effort of NASA and the Japan
Aerospace Exploration Agency. “Many
satellites can see the top of a hot tower, but
what’s special about this satellite’s
Precipitation Radar is that it gives you
‘X-ray vision’ so you can see inside
a hot tower,” Kelley said. To compile
global statistics, the radar needs to be orbiting
the Earth.
After compiling the statistics, Kelley and
Stout found a tropical cyclone with a hot tower
in its eyewall was twice as likely to intensify
within the next six hours than a cyclone that
lacked a tower. The “eyewall” is the
ring of clouds around a cyclone’s central
eye. Kelley and Stout considered many alternative
definitions for hot towers before concluding the
nine-mile height threshold was statistically
significant.
Funding for the research was provided by
NASA’s Earth Science Enterprise. The
Enterprise strives to advance Earth System
Science and to improve the prediction of climate,
weather and natural hazards from the unique
vantage point of space.
For more information about the research and
images on the
Internet, visit:
http://www.gsfc.nasa.gov/topstory/2004/0112towerclouds.html
For information about the TRMM Satellite on
the Internet,
visit:
http://trmm.gsfc.nasa.gov
http://www.eorc.nasda.go.jp/TRMM
For information about NOAA’s National
Hurricane Center, visit:
http://www.nhc.noaa.gov
For information about Hurricane Bonnie,
visit:
http://www.nhc.noaa.gov/1998bonnie.html
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Contacts:
Elvia Thompson
Headquarters,
Washington
Phone: 202/358-1696
Rob Gutro
Goddard Space Flight Center, Greenbelt, Md.
Phone: 301/286-4044
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An Unusually Deep Convective Tower in
Hurricane Bonnie as Bonnie
Intensified
This TRMM Precipitation Radar overflight of
Hurricane Bonnie shows an 11 mile high
“tower” cloud perched on the eyewall
of the storm. Bonnie was observed on August 22,
1998, a few days before it struck North Carolina.
The 3D volume represents the raining region
inside the clouds of the hurricane. This 3D
volume contains all of the locations where the
rain rate was at least 0.08 inches per hour. The
eye and eyewall are labeled on the image of
surface rain rate. Cyclone intensification may be
associated with the presence a tower cloud in the
cyclone’s eyewall. CREDIT: NASA /
JAXA
High-Resolution
Image
Typhoon Paka’s Hot
Towers
This animation of data from the TRMM
satellite’s Precipitation Radar shows the
large towering convective clouds or “Hot
Towers” in Super Typhoon Paka on Dec. 10,
1997. CREDIT: NASA’s Scientific
Visualization Studio
Hurricane Bonnie’s Hot
Towers
Hurricane Bonnie’s cumulonimbus storm
clouds towered 11 miles (18 km) above the eye of
the storm. The height in this image is
exaggerated for clarity, and colors correspond to
surface precipitation from blue (light) to red
(heavy). CREDIT: NASA’s Scientific
Visualization Studio
High-Resolution
Image
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