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Dispersal
Mon Nov 21, 2005
Listen in RealAudio 
How far and fast would a chemical attack spread through New York City? That is the question scientists with the Homeland Security-sponsored Urban Dispersion Program are attempting to answer. Hi, I’m Bryan Yeaton for The Weather Notebook. From New York, Val Wang has our story.
During 6 days in August, the scientists released harmless tracer gases from various locations around midtown Manhattan, and then measured their dispersion through 180 samplers in and on buildings, and in the subways. Brian Colle, Associate Professor of Atmospheric Science at Stony Brook University, had the job of predicting the wind patterns for the scientists who were releasing the chemicals and collecting the data.
"From a meteorological point of view, I think we underestimated the power of the city, so to speak, to drive its own internal circulation. This was in August where in the early morning hours the winds are quite weak and therefore a lot of the winds around New York City are driven by the differential heating between the urban heat island and the surrounding cooler waters."
New York City's deep canyons also make it a fascinating study. As each building warms the air around it and directs airflow upwards, the winds become erratic, sometimes blowing north at the rooftop level and south at ground level. Seen through a meteorologist's eyes, the natural world in New York City can be just as complex as its social world.
"It's very complex. The next time you're in New York City, that's when you begin to appreciate that the flow is effectively being channeled down these narrow canyons."
The four-year study will not only help scientists prepare for terrorist attacks, but also learn about how air flows in and around a city. From New York City, I’m Val Wang for The Weather Notebook.
Our show is funded by Subaru of America.
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