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July-August 2006

short takes

An overview of projects throughout the organization

Mt. Pinatubo
Hurricane Ophelia was the eighth hurricane of the record season of 2005.

Hurricanes and climate change. Global warming accounted for around half of the unusual warmth in the waters of the tropical North Atlantic during the record hurricane season of 2005, according to a recent analysis by CGD's Kevin Trenberth and Dennis Shea. The study contradicted recent claims that natural cycles are responsible for the upturn in Atlantic hurricane activity since 1995.

Kevin and Dennis's research focused on an increase in ocean temperatures. During much of last year's hurricane season, sea-surface temperatures (SSTs) across the tropical Atlantic between 10 and 20°N, which is where many Atlantic hurricanes originate, were a record 1.7°F above the 1901–70 average.

By analyzing worldwide data on SSTs since the early 20th century, Kevin and Dennis were able to assess the causes of the increased temperatures. Their calculations showed that global warming explained about 0.8°F of this rise. Aftereffects from the 2004-05 El Niño accounted for about 0.4°F. The Atlantic multidecadal oscillation (AMO), a 60- to 80-year natural cycle in SSTs, explained less than 0.2°F of the rise. The remainder was due to year-to-year variability in temperatures.

Previous studies have attributed the warming and cooling patterns of North Atlantic ocean temperatures in the 20th century—and associated hurricane activity—to the AMO. But Kevin, suspecting that global warming was also playing a role, looked beyond the Atlantic to temperature patterns throughout Earth's tropical and midlatitude waters. He subtracted the global trend from the irregular Atlantic temperatures—in effect, separating global warming from the Atlantic natural cycle. The results show that the AMO is actually much weaker now than it was in the 1950s, when Atlantic hurricanes were also quite active. However, the AMO did contribute to the lull in hurricane activity from about 1970 to 1990 in the Atlantic.

The study appeared in the June 27 issue of Geophysical Research Letters.

Mt. Pinatubo
The shelled pteropod is a small planktonic marine snail that may be unable to sustain its populations as the oceans become increasingly acidic. (Photo courtesy Victoria Fabry, California State University, San Marcos.)

Ocean acidification. ISSE's Joanie Kleypas and a team of researchers have released a report about the dramatic impacts of carbon dioxide emissions on ocean chemistry. The increasing acidity of the oceans is threatening marine organisms, including corals, that secrete skeletal structures and support oceanic biodiversity.

The July report, "Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers," summarizes the known effects of increased atmospheric carbon dioxide on these organisms, known as marine calcifiers, and recommends future research for determining the extent of the impacts. It warns that oceans worldwide have absorbed approximately 118 billion metric tons of carbon between 1800 and 1994. This is leading to the biggest changes in ocean chemistry in at least 650,000 years. The increased acidity of the oceans lowers the concentration of the carbonate ion, a building block of the calcium carbonate that many marine organisms use to grow their skeletons and create coral reef structures.

"It is clear that seawater chemistry will change in coming decades and centuries in ways that will dramatically alter marine life," says Joanie, the report's lead author. "But we are only beginning to understand the complex interactions between large-scale chemistry changes and marine ecology."

The report follows a workshop funded by NSF and NOAA and hosted by the U.S. Geological Survey Integrated Science Center in St. Petersburg, Florida. Download a copy of the report.

Stratospheric temperatures. Temperatures in the lower stratosphere have dropped to record lows over the past 20 years. This is largely due to ozone depletion, but recent research suggests that other factors are involved as well. ACD's Bill Randel took part in a modeling study, led by NOAA's Venkatachalam Ramaswamy, to consider the impact on stratospheric temperatures of natural factors (volcanic aerosols and the 11-year solar cycle) as well as human-induced factors (trends in greenhouse gases and aerosols, ozone variations, and land use changes).

The team conducted five experiments to look at various blends of human and natural influences. A principal goal was to determine why the lower stratosphere has chilled in fits and starts, and why sharp spikes in the early 1980s and 1990s were followed by periods with little change later in each decade.

The scientists found that the irregular cooling trend could be explained only when all factors are included. The two spikes were related to the volcanic eruptions of El Chichon (1982) and Mt. Pinatubo (1991). Aerosols from each eruption triggered warmings in the lower stratosphere that lasted about two years, followed by sharp coolings. Later in each decade, there was little change in stratospheric temperature because the cooling influence of ozone depletion was counteracted by a warming influence from the strengthening solar cycle, which peaked in 1991 and 2001.

The study, which used models from NOAA's Geophysical Fluid Dynamics Laboratory, appeared in the February 24 issue of Science.

Forecasting floods. Floods are a major weather-related hazard, claiming the lives of about 100 people in the United States in an average year and causing more than $2 billion in damages. Decision makers have a pressing need for reliable flash flood forecasts, especially as urban areas expand and development encroaches on flood plains. Networks of gauging systems can provide communities with some degree of advance warning about rising waters, but the networks typically lack the dense number of gauges required to provide accurate flash flood forecasting.

A team of RAL researchers examined whether it is possible to generate accurate forecasts with a hydrologic model that incorporates high-resolution weather radar data, physically based flood modeling, and a storm nowcast system. The team—Hatim Sharif (now at the University of Texas), David Yates, Rita Roberts, and Cynthia Mueller—used this approach to examine two heavy rains in 2001 in the Harvard Gulch watershed near Denver. A small catchment that can flood quickly, the gulch is particularly challenging for forecasters.

The team's simulation proved successful, with a difference of only 9% between the simulation of the peak discharge and the actual peak discharge estimate based on high water marks. The researchers concluded that, although more work is needed, radar data, hydrologic modeling, and nowcasting have the potential to provide accurate information about flash floods to decision makers in real time.

The research was published in the American Meteorological Society's Journal of Hydrometeorology in February.

Mt. Pinatubo
TeraGrid is coordinated through the University of Chicago/Argonne National Laboratory, working with sites at Indiana University, National Center for Supercomputing Applications, NCAR, Oak Ridge National Laboratory, Pittsburgh Supercomputing Center, Purdue University, San Diego Supercomputer Center, and Texas Advanced Computing Center. (Image courtesy TeraGrid.)

Joining the TeraGrid. NCAR has joined the TeraGrid, a network of supercomputers and other devices that comprises the nation's most advanced infrastructure for open scientific research. As a TeraGrid partner site, NCAR will offer atmospheric researchers increased access to the organization's high-performance computing, climate data, and tools for data analysis and visualization.

CISL worked closely with the TeraGrid to establish the partnership.

The TeraGrid, sponsored by NSF, uses high-performance networks and grid middleware to integrate supercomputers, data repositories, and special-purpose data analysis facilities around the country. A common set of specifications, software, and physical equipment creates a coordinated work environment that enables researchers throughout the United States to collaborate on especially challenging scientific questions.

"Joining the TeraGrid is an important strategic step for NCAR," says NCAR director Tim Killeen. "The demand for cyberinfrastructure resources by the geosciences clearly exceeds the capacity of any single supercomputing center."

After months of preparation, a joint NCAR/TeraGrid team transferred the first bits of data over the TeraGrid link on May 15. A new, dedicated TeraGrid data server has been installed at NCAR, and plans are being developed to connect an experimental storage cluster and provide access to select supercomputing resources.

For more about the TeraGrid.

In this issue...

A new eye on storm formation

NCAR names five new senior scientists

New Delphi coordinator takes over

SOARS and RESESS protégés busy with research

Less load for the landfill: FREEcycle stores; ACD's "green" move

Short Takes

Delphi Question: Public events in the FL0 courtyard

Just One Look


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