October 17, 2002
For more information on these science news and feature
story tips, please contact the public information
officer at the end of each item at (703) 292-8070.
Editor: Josh Chamot
Contents of this News Tip:
New Model Enhances
National Hurricane Prediction System
Scientists know that while most hurricanes rapidly
weaken after landfall, mainly because their source
of evaporating water dries up, some storms are able
to persist and cause further damage. Researchers have
now found that under certain conditions, inland water
sources less than two-feet-deep are enough to sustain
storms and lead to further damage.
Supported by the National Science Foundation (NSF),
oceanographer Isaac Ginis of the University of Rhode
Island (URI) Graduate School of Oceanography and colleagues
studied the effect of land-surface water on hurricane
intensity.
Ginis, along with URI oceanographer Lewis Rothstein,
developed a computer model to predict the hurricane
intensity. They coupled their model with one created
by the National Oceanic and Atmospheric Administration's
(NOAA) Geophysical Fluid Dynamics Laboratory to provide
a more efficient framework to consider atmosphere-ocean
interaction during storms, and more accurately predict
storm intensity. The coupled model has become an official
component of the national hurricane prediction system
used to forecast Atlantic and Gulf of Mexico tropical
storms and hurricanes.
Previous studies of land-falling hurricanes used fixed
underlying surface conditions. Ginis' study used a
newer model that includes surface temperature changes
and their influence on surface heat, hurricane structure
and hurricane intensity. The scientists also used
a range of water depths and surface roughness to allow
an array of surface conditions.
The study showed that during hurricane landfall over
water-covered land, large local surface cooling occurs
near the hurricane core region. The surface cooling
reduces evaporation, considerably reducing the hurricane
intensity. The reduction depends on the presence and
depth of surface water. With a two-foot layer of surface
water, the hurricane will maintain its intensity,
but over dry land, the storm collapses.
Ginis, along with URI oceanographer Lewis Rothstein,
developed a computer model to predict the hurricane
intensity. They coupled their model with one created
by NOAA's Geophysical Fluid Dynamics Laboratory to
provide a more efficient framework to consider atmosphere-ocean
interaction during storms, and more accurately predict
storm intensity. The coupled model has become an official
component of the national hurricane prediction system
used to forecast Atlantic and Gulf of Mexico tropical
storms and hurricanes. [Cheryl Dybas]
Top of Page
Hurricane Isidore
Proves Perfect Subject for Study of Rapidly Intensifying
Storms
The season's second tropical whirlwind to reach hurricane
strength gave hurricane hunters the opportunity to
monitor and measure a tropical storm as it rapidly
intensifies.
Supported by NSF, scientist Nick Shay of the University
of Miami, along with atmospheric researcher Peter
Black of NOAA's hurricane research division, are studying
how deep layers of warm surface water in the ocean
help hurricanes to rapidly intensify - one of the
most difficult situations to forecast and one of the
most dangerous for coastal residents.
The scientists dropped a series of ocean probes from
hurricane hunter aircraft as Isidore gained strength.
Released in Isidore's projected path in the southern
Gulf of Mexico, the probes measured ocean temperature
and currents down to 200 meters (about 650 feet),
the depth at which hurricane winds usually churn up
colder water and cool the overall temperature of water
below the storm.
"When Isidore is over the Gulf Stream, its warm water
extends below to great depths, not allowing Isidore's
winds to cool the surface," said Shay. "That in turn
keeps the heat reservoir intact and allows further
intensification of a hurricane."
Shay and Black will measure differences in the ocean's
temperature structure during three phases of tests.
The results, say the scientists, will clarify the
ocean's role in hurricane intensification and may
lead to a greater ability to predict when and how
much a storm may intensify - a challenge considered
to be the next step in hurricane forecasting. [Cheryl
Dybas]
Top of Page
Lowered Methane
Emissions Could Reduce Both Global Warming and Air
Pollution
Reducing methane gas emissions by half could alone
reduce air pollution and global warming, according
to a new study by scientists at Harvard University,
Argonne National Laboratory, and the Environmental
Protection Agency. In the NSF supported-study, researchers
directly link methane to the production of ozone in
the troposphere, the part of the atmosphere that extends
from the Earth's surface upwards about 7.5 miles.
Ozone is the primary constituent of smog, and both
methane and ozone are significant greenhouse gases.
In the October issue of Geophysical Research Letters,
Arlene M. Fiore of Harvard and her colleagues simulated
effects of methane on climate using emissions projections
from the United Nations Intergovernmental Panel on
Climate Change (IPCC). From their findings, the researchers
suggest that global reduction of methane emissions
will simultaneously decrease ozone pollution and greenhouse
warming.
The researchers find that reducing methane emissions
from human activities by 50 percent would have a greater
impact on global tropospheric ozone than would a comparable
reduction in nitrogen-oxide emissions from human activities.
Reducing surface nitrogen-oxide emissions does effectively
improve air quality by decreasing surface ozone levels,
but this impact tends to be local, and does not yield
as much benefit from greenhouse warming.
Human-derived sources of methane include rice production,
leaks of natural gas from pipelines and herds of cattle.
Natural sources include wetlands, termites, oceans
and methane trapped in ice on the sea floor. A baseline
study in 1995 showed that 60 percent of methane emissions
to the atmosphere were the result of human activity.
However, according to the researchers, aggressive emission
controls aimed at lowering ozone-based pollution both
in the United States and Europe could be offset by
rising emissions of methane and nitrogen oxides from
developing countries.
The study was also funded by the Environmental Protection
Agency (EPA), and the National Aeronautics and Space
Administration (NASA). [Cheryl Dybas]
Top of Page
|