Tar, asphalt, brick and concrete are better conductors of heat than the vegetation of the rural area. The canyon structure that tall buildings create enhances the warming. During the day, solar energy is trapped by multiple reflections off the buildings while the infrared heat losses are reduced by absorption. The urban heat island effects can also be reduced by weather phenomona. The temperature difference between the city and surrounding areas is also a function of the synoptic scale winds.
Strong winds reduce the temperature contrast by mixing together the city and rural air.
The urban heat island may also increase cloudiness and precipitation in the city, as a thermal circulation sets up between the city and surrounding region. The image has a spatial resolution of approximately 1 km. The warmer the body, the greater the amount of radiant energy it emits. A map is overlain the image to help orient you to the geography of the region. This Java Applet will help you learn to identify urban heat islands on satellite images.