Meteorology: Understanding the Atmosphere Ackerman and Knox |
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Urban Heat IslandIt has been known for some time that cities are generally warmer than the surrounding, more rural areas. Because of this relative warmth, a city may be referred to as an urban heat island. The reason the city is warmer than the country comes down to a difference between the energy gains and losses of each region.The urban heat island is clearly evident in a statistical study of surface air temperatures. It is also apparent on cloud-free satellite images, as the above 11 micrometer image produced with the Advanced Very High Resolution Radiometer (AVHRR) shows. The image has a spatial resolution of approximately 1 km. At this wavelength, the AVHRR measures the amount of radiant energy emitted by the surface and the tops of clouds, which is proportional to the temperature of the emitting body. The warmer the body, the greater the amount of radiant energy it emits. White portions of the image represent cold objects (e.g., cloud tops) and dark regions are warm areas. You may have to hit "SHIFT RELOAD" or "SHIFT REFRESH" A map is overlain the image to help orient you to the geography of the region.
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