September 15, 2010
The air temperature for an area is taken by an Automated Surface Observing Station,(ASOS pictured above) , most of which are located at airports. The National Weather Service has a network of 900 ASOS stations nationwide. The thermometer used to take the temperature is an electric thermometer that is housed in a shelter that sits about 5 feet off of the ground. The temperature at the earth's surface can be as much as 5 degrees warmer or cooler than the air temperature just 5 feet above. This happens because the Earth's surface is a great radiator of long wave radiation, but air is a poor absorber of long wave radiation. The thermometer is housed in a shelter so that it gets a measurement of the air temperature that isn't affected by direct rays from the sun or cold winter winds. Pretty neat 'eh?