Weather Making Cities – Description

ambience : sounds from a metropolitan area

Cities not only generate air pollution, well it turns out that they make their own weather, too. I’m Jim Metzner, and this is the Pulse of the Planet. Cities are often hotter than the rural areas around them. Researchers have found out some reasons why.

“The heat island effect is a result of the fact that cities are warmer than their surrounding rural counterparts. And this is because of the fact that we have urban areas with pavements, and concrete, and asphalt, and building rooftops which are significantly warmer than surrounding rural areas, where there’s vegetation.”

Dale Quattrochi is a senior scientist with the NASA’s Marshall Space Flight Center. He tells us that the heat island effect can act like a pump that drives a city’s weather.

“What we’re actually finding is that because the city is hotter, that is, the surface of the city is hotter than non urbanized areas, because of the surfaces in the city that actually absorb sunlight throughout the day – what happens is there is a chimney effect that is set up over the urban area itself. And this chimney effect pumps up hot air into the lower atmosphere, and what happens is it essentially sets up a low-pressure system over the city. And this low-pressure system sucks in, or brings in cooler air from the outside. And cooler air is denser than warmer air, which means that it falls down into this chimney. As it falls down into the chimney effect, it gets heated up – of course hot air rises. And as hot air rises, it condenses, it forms clouds and it rains. And it rains over the city or down wind of the city, as we’ve found.”

In our next program we’ll hear what cities can do to try to lessen the heat island effect.

Pulse of the Planet is presented by the National Science Foundation. I’m Jim Metzner.

music

Weather Making Cities - Description

Meteorological conditions in urban areas are greatly influenced by the cityscape.
Air Date:08/20/2003
Scientist:
Transcript:

ambience : sounds from a metropolitan area

Cities not only generate air pollution, well it turns out that they make their own weather, too. I'm Jim Metzner, and this is the Pulse of the Planet. Cities are often hotter than the rural areas around them. Researchers have found out some reasons why.

"The heat island effect is a result of the fact that cities are warmer than their surrounding rural counterparts. And this is because of the fact that we have urban areas with pavements, and concrete, and asphalt, and building rooftops which are significantly warmer than surrounding rural areas, where there's vegetation."

Dale Quattrochi is a senior scientist with the NASA's Marshall Space Flight Center. He tells us that the heat island effect can act like a pump that drives a city's weather.

"What we're actually finding is that because the city is hotter, that is, the surface of the city is hotter than non urbanized areas, because of the surfaces in the city that actually absorb sunlight throughout the day - what happens is there is a chimney effect that is set up over the urban area itself. And this chimney effect pumps up hot air into the lower atmosphere, and what happens is it essentially sets up a low-pressure system over the city. And this low-pressure system sucks in, or brings in cooler air from the outside. And cooler air is denser than warmer air, which means that it falls down into this chimney. As it falls down into the chimney effect, it gets heated up - of course hot air rises. And as hot air rises, it condenses, it forms clouds and it rains. And it rains over the city or down wind of the city, as we've found."

In our next program we'll hear what cities can do to try to lessen the heat island effect.

Pulse of the Planet is presented by the National Science Foundation. I'm Jim Metzner.

music