|
NASA
LOOKS A HURRICANE’S TEMPERATURE IN THE EYE
Last
year, NASA researchers took the temperature of the eye of
Hurricane Erin to determine how a hurricane’s warm center
fuels the strength of storms. The new data is helping scientists
understand the inner workings of hurricanes at very high altitudes,
and will improve future hurricane forecasts.
The
researchers found that the warmest portion around a hurricane’s
eye is approximately 3.5 miles high and that area in the eye
corresponds with falling pressure, which is what causes the
winds to spiral inward at destructive speeds.
During
September 2001 while flying over the North Atlantic Ocean,
scientists aboard NASA’s ER-2 aircraft dropped eight
sensors into the area around Hurricane Erin’s eye, containing
the strongest thunderstorms and winds, and warmest temperatures.
Variations in temperatures within a hurricane provide clues
about the storm’s intensity. For example, a warm center
marked by a large temperature contrast compared to the rest
of the hurricane is a sign of a strong storm.
The
sensors measured temperature, air pressure and winds as they
fell through the hurricane and transmitted their data back
to the ER-2 aircraft. For the first time, the data allowed
scientists to create a comprehensive 3-dimensional image of
the complete inner core (including the eyewall and the eye)
of a hurricane, giving scientists a better look at how heat
from warm, rising air spreads out in the storm’s center.
The warm, humid, rising air is the key to a hurricane’s
power. This rising air draws in air from the surface to take
its place, and creates winds.
“Scientists
can obtain a detailed look at a hurricane’s heat engine
(the warm temperatures that power a storm) by combining the
aircraft data with that from satellites such as NASA’s
Tropical Rainfall Measurement Mission,” said Jeff Halverson,
a scientist from NASA’s Goddard Space Flight Center,
Greenbelt, Md., and the University of Maryland Baltimore County.
“The
data from the sensors and the satellite have given us a view
of the eye’s warm air, the rain clouds that warm the
air through condensation, and the spiraling surface winds
which in turn create the rain clouds. We have assembled all
this data in a three dimensional rendition of the hurricane
which is akin to taking a detailed ‘CAT scan’ of
the storm,” Halverson said.
“We
found that this storm had a very warm eye, from the ocean
to the top of the lower atmosphere at around 10 miles altitude,”
said Halverson. The warmest part of Erin’s eye was almost
21 degrees (Fahrenheit) warmer than the surrounding air, a
dramatic difference from the air around it. Above 7.5 miles
high, the eye’s temperature dropped quickly to the same
temperature as the air outside the eye.
The
warming temperatures within the hurricane’s eye make
the air lighter, so air pressure eases on the surface and
falls. When air is cold, the air molecules are dense, and
air is heavier. The falling pressure in the hurricane’s
eye is what creates swirling destructive winds.
The
experiment also discovered that strong rising air currents
in Erin caused the tropopause (top of the lower atmosphere)
to “bubble up” or bend, south of the eye’s
center. This is indicative of the strength of Hurricane Erin,
which was a Category 3 storm at this time.
There
are five categories in which hurricanes are classified, the
fifth being the most devastating. Category 3 hurricanes, such
as Erin have winds between 111-130 mph, and can bring a storm
surge of water (wind driven water above tide level) between
9-12 feet to shorelines.
Halverson
will be presenting these findings at the AMS Hurricane and
Tropical Meteorology Conference in San Diego, Calif. on Tuesday,
April 30, 2002 at 9:00 a.m. Pacific time in a session titled
“Thermal Structure of Hurricane Erin’s Core Using
Dropsonde Data From 68,000 Feet and Comparison with AMSU Satellite
Measurements.”
NASA
research was funded through NASA Headquarters and the CAMEX-4
Hurricane Program.
EDITORIAL
NOTE: Media should see Claudia Gorski at conference registration.
There will not be an official press room. For more information:
http://www.ametsoc.org/AMS/meet/FAINST/25hurr.html
Back
to Top
|
