Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cities incite thunderstorms

13.08.2007
Summer thunderstorms become much more fierce when they collide with a city than they would otherwise be in the open countryside, according to research led by Princeton engineers.

Alexandros A. Ntelekos and James A. Smith of Princeton University’s School of Engineering and Applied Science based their conclusion on computer models and detailed observations of an extreme thunderstorm that hit Baltimore in July of 2004.

Their modeling suggests that the city of Baltimore experienced about 30 percent more rainfall than the region it occupies would have experienced had there been no buildings where the city now sits.

While thunderstorms are thought of as being purely forces of nature, the Princeton research suggests that man’s built environment can radically alter a storm’s life cycle.

A storm of the intensity of the 2004 event in Baltimore is extremely rare, occurring only once every 200 years or so. However, climate change is expected to make such events more frequent, according to the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC).

“Precipitation events like gully-washing rainstorms are expected to increase in intensity as the world warms due to the buildup of greenhouse gases,” said Michael Oppenheimer, a lead author on the IPCC report and the Albert G. Milbank Professor of Geosciences and International Affairs at Princeton. “This is just the sort of research that combines science, engineering, and social response that may allow us to better cope with the future, warmer climate. I hope it will also serve as a warning about the complexity of adaptation, and therefore, as a goad to policymakers to act more urgently to stabilize the climate.”

In yesterday’s intense storm in New York City -- which played havoc with subways, street traffic, and airports – about three inches of rain fell in one hour. In the 2004 storm that the researchers studied, about six inches fell within two hours.

“The storm that occurred yesterday in New York City is an example of the sort of event that we expect more of in the future,” said Oppenheimer. “The disruptive effect was quite obvious.”

Observational data shows that, during the 2004 storm, parts of Baltimore experienced as many lightning strikes in the space of two hours as they normally receive during the course of a year.

Much of the lightning during the 2004 storm wrapped around the western edges of Baltimore and Washington, D.C., to the south. “It’s as if all of a sudden the lightning can ‘feel’ the city,” said Ntelekos, a Princeton graduate student in civil and environmental engineering who is a fellow with the Woodrow Wilson School’s Science, Technology, and Environmental Policy (STEP) program.

The interaction between storm and city has serious consequences for urbanites as well as policymakers.

“This means that warm-season thunderstorm systems will probably increasingly lead to more flash flooding, which can be very dangerous,” said Smith, a professor of civil and environmental engineering at Princeton.

Hydrologists have observed evidence in the past that urban environments alter the behavior of storms. But they have mostly noted average increases in rainfall over long periods of time. Until now, they have not made observations of specific extreme storms because they lacked the right tools to do so.

The National Science Foundation-funded research by Ntelekos and Smith pieced together many different pieces of observational information on lightning strikes, rainfall, clouds and aerosols -- which they combined with analyses based on computer models of the atmosphere.

The combined data yielded surprising conclusions. For example, neighboring cities also can affect the behavior of a storm. The Ntelekos-Smith research showed that the 2004 storm over Baltimore was partially affected by the neighboring urban environment of Washington D.C. as air from the south became more turbulent when passing over it. This made the air mass particularly ripe for a storm by the time it reached Baltimore.

The scientific consensus so far has been that, during a storm, greater rainfall occurs on the downwind part of the city than on the upwind side.

However, the researchers found that during the 2004 Baltimore storm, the western part of the city -- not the upwind, northern part -- was hit harder by rainfall and thus extreme flooding, according to Ntelekos.

“Previous studies basically came from cities where the terrain was simple, where you had a town in the middle of nothing -- no mountains, no water,” he said. “But most of the hub cities are close to either mountains or water as well as being close to other cities. So we have to understand how extreme thunderstorms behave over complex terrains.”

Ntelekos and Smith are presenting some of their research this week at a workshop sponsored by MIRTHE, a National Science Foundation Engineering Research Center at Princeton University.

Exactly how does the urban environment alter the evolution of thunderstorms" The researchers described three mechanisms:

Urban heat islands: Cities produce heat and are often 2 to 5 degrees Fahrenheit hotter than the surrounding environment. In milder storms, this “heat island” can provide fuel for a modest thunderstorm. But in their study of the 2004 thunderstorm, the Ntelekos and Smith found that the heat island had little effect because high winds leveled temperatures.

Urban canopies: While forests have tree canopies, cities have building canopies. The height and placement of buildings alters a storm’s low-level wind field, a key ingredient in its behavior. The tall buildings increase wind drag on the city, resulting in vertical velocities – essentially a boiling action – that can enhance rainfall. The urban canopy had a large effect during the 2004 storm, the researchers found, which was exacerbated all the more by the presence of the Chesapeake Bay to the east.

Urban aerosols. These are essentially minuscule particles in the atmosphere that are at elevated levels in urban environments due to industrial and automobile emissions. Traditionally, researchers have thought that air pollution tends to suppress precipitation. But Ntelekos and Smith believe their research points to the possibility that urban aerosols actually increase rainfall.

Ntelekos plans to build on his Baltimore research in a more detailed study of the effect of aerosols on thunderstorms in New York City. That research will be a testbed for laser-based sensor technologies being developed by Princeton’s MIRTHE center, which is charged with developing next-generation sensor technology for the environmental monitoring, medical diagnostics and national security.

Teresa Riordan | EurekAlert!
Further information:
http://www.princeton.edu

More articles from Ecology, The Environment and Conservation:

nachricht Successful calculation of human and natural influence on cloud formation
04.11.2016 | Goethe-Universität Frankfurt am Main

nachricht Invasive Insects Cost the World Billions Per Year
04.10.2016 | University of Adelaide

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>