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Tip Sheet: Explaining Hurricane Behavior, Impacts, and Possible Links to Global Warming
June 27, 2007
BOULDER—Researchers, forecasters, and the public are avidly watching as the 2007 hurricane season unfolds. Seasonal forecasts issued in May by NOAA and Colorado State University point to a busier-than-usual Atlantic season, in keeping with trends since 1995. However, the UK Met. Office is calling for a quieter-than-usual North Atlantic based on high-resolution modeling (a different approach than the statistics-based tools used by US forecasters).
After the devastating 2004 and 2005 hurricane seasons, many Americans saw 2006 as a calm year, since there were no major U.S. landfalls. However, there was enough action out to sea to keep the Atlantic's overall tally of nine named storms close to the long-term average. The northeast Pacific was busier than usual, with 18 named storms and a November as active as any on record. And in the central Pacific, Ioke—which reached Category 5 strength twice as a hurricane and once as a typhoon—became the first tropical cyclone anywhere to sustain Category 4 strength for more than eight consecutive days.
Scientists at the National Center for Atmospheric Research (NCAR) and its parent organization, the University Corporation for Atmospheric Research (UCAR), closely study hurricanes, typhoons, and other tropical cyclones (the term varies depending on geography, but refers to the same type of storm). The scientists use advanced computer models and draw on a wide range of observations to study the early development of cyclones, track the intense storms, and even predict major impacts before landfall.
Experts are available to explain
- whether global climate change is augmenting hurricane strength and what the future may hold;
- what may cause a hurricane to spin up initially, gain or lose intensity, or veer on a new course;
- how even weak tropical storms and hurricanes can lead to devastating floods;
- how scientists can help utilities and local governments to anticipate and prepare for hurricane impacts.
UCAR also offers background information on the Web about hurricanes and other cyclones (see the Background section of this tip sheet, below).
Experts at NCAR
Formation, intensity, and motion
NCAR Scientist, Mesoscale and Microscale Meteorology
Division and Research Applications Laboratory
Davis studies the systems that lead to hurricanes, thunderstorms, and other heavy rainfall events. He uses observations and sophisticated computer models to analyze the evolution of these systems. Recently Davis has focused on the role of weak nontropical disturbances in fostering the development of some tropical storms and hurricanes.
NCAR Scientist, Earth Observing Laboratory
Lee is a specialist in hurricane winds and intensity. He is the chief scientist for NCAR's ELDORA, an airborne Doppler radar, which captures detailed images of precipitation and winds from hurricanes and severe thunderstorms. Lee has developed a mathematical technique to extract more information out of radar depictions of hurricane eyewalls and other intense, fast-changing weather systems.
Climate change, global warming
NCAR Scientist, Mesoscale and Microscale
Holland is director of NCAR's Mesoscale and Microscale Meteorology Division, which studies weather on the local and regional scale. His background is in tropical meteorology and severe weather, and his specialties include hurricane structure and behavior. Holland coauthored a paper in Science last year showing that the frequency of Category 4 and 5 cyclones has nearly doubled since 1970. He also is an expert on the torrential rains and other effects produced as tropical cyclones move inland.
NCAR Scientist, Climate and Global Dynamics
Trenberth's research emphasizes the analysis of observational data. He has been on the forefront of scientists examining the question of whether climate change, including global warming, is affecting the intensity of hurricanes and other tropical cyclones. He also is an expert on El Niño and the water cycle.
UCAR Hydrometeorologist, Cooperative
Program for Operational Meteorology, Education and Training
Kelsch specializes in weather events involving water, such as floods, droughts, rain, hail, and snow. He has studied some of the biggest U.S. flood events connected to hurricanes and tropical storms.
NCAR Visiting Scientist, Research Applications Laboratory, Computational & Information
Bush is an expert on computer simulations of energy and transportation infrastructure. Based at Los Alamos National Laboratory, he is spending two years at NCAR working to incorporate better weather data into the hurricane damage models developed at Los Alamos for the federal government. During last year's major hurricane threats, Bush worked closely with colleagues at NCAR and Los Alamos to convert forecasts of wind, rain, and storm surge into experimental damage probabilities for utility generation stations, substations, and power lines.
NCAR Visiting Scientist, Center for Capacity Building
Kelman's research focuses on hurricanes and other disasters, their effects on people and infrastructure, and the vulnerabilities of communities. He is also interested in disaster deaths, analyzing the individuals who are most likely to die in disasters and why.
The role of global warming
Recent studies using computer models and observations going back to the 1970s suggest that, because of warmer sea-surface temperatures and moister air, more energy goes into the showers and thunderstorms that feed hurricanes, pushing more of them into the extreme category. Follow these links for research news on the relationship between hurricanes and global warming:
Most computer models designed to study global climate cannot depict the small-scale air motions at the heart of a hurricane. Weather prediction models can do this, but they don't extend far enough in time or space to show how future climate change will affect hurricanes. A project at NCAR is linking global models with regional models in order to better understand how cyclones and other tropical disturbances vary over time. Meanwhile, NCAR is refining the Advanced Research WRF, its version of the multiagency Weather Research and Forecasting model. The ARW was among the most accurate models in projecting the track and intensity of 2005's major Atlantic hurricanes. Follow these links to view last year's ARW forecasts and to learn more:
In August 2005, NCAR researchers and colleagues from the French space
agency began launching specialized balloons, called driftsondes, carrying
miniaturized weather instruments to detect hurricanes as they emerge
over the far-eastern Atlantic. This critical region is out of range
of U.S. hunter-hurricane aircraft. The driftsondes are probing
weak weather systems, called easterly waves, that serve as seedlings
for hurricanes. Dozens of these waves move across Africa into the Atlantic
between about 10 and 20 degrees north. The project relies on new technology
to provide early warning of potentially dangerous storms.
Hurricanes, Typhoons, and Cyclones
What's the difference between a hurricane and a tropical cyclone?
What wind speed correlates with each hurricane category? Follow
this link to find hurricane basics, images, and a research
roundup, plus numerous links to additional resources within and
beyond NCAR and UCAR.
Related sites on the World Wide Web
Current Conditions from NOAA's National Hurricane Center
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