Air temperature is the most widely measured quantity in the atmosphere according to the National Weather Service. People plan their lives around the temperature, from picking out their clothes to planning daily activities. With temperature being so important, I think it’s necessary to understand how to properly measure it. I think you would be surprised at how many people, including professional meteorologists, don’t quite follow the general guidelines laid out by the National Weather Service.
The following directions apply to all types of thermometers, from classic mercury thermometers to new-age digital temperature sensors.
1. Place the thermometer 5 feet above the ground (+/- 1 ft.). A thermometer too low will pick up excess heat from the ground and a thermometer too high will likely have too cool of a temperature due to natural cooling aloft. 5 ft. is just right.
2. The thermometer must be placed in the shade. If you put your thermometer in full sunlight, direct radiation from the sun is going to result in a temperature higher than what it should be.
3. Have good air flow for your thermometer. This keeps air circulating around the thermometer, maintaining a balance with the surrounding environment. Therefore, it is important to make sure there are no obstructions blocking your thermometer such as trees or buildings. The more open, the better.
4. Place the thermometer over a grassy or dirt surface. Concrete and pavement attract much more heat than grass. That is why cities are often warmer compared to suburbs. It is recommended to keep the thermometer at least 100 ft. from any paved or concrete surfaces to prevent an erroneously high temperature measurement.
5. Keep the thermometer covered. When precipitation falls, you do not want your thermometer to get wet as that could permanently damage it. A Stevenson screen is a great place to store thermometers and other instruments as they provide cover as well as adequate ventilation. If you can’t get one, a simple solar radiation shield is adequate.
And that’s it. Now you are all temperature measuring experts so let’s get out there and start taking some readings!
Stevenson Screen Source: http://en.wikipedia.org/wiki/Stevenson_screen#mediaviewer/File:Stevenson_screen_exterior.JPG
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