Placing the Instruments
Now that we have a set of weather instruments, where do we place them for the most accurate and most representative readings?
First of all, thermometers must never be placed in the sun. It might be fun to put a thermometer out onto a tennis court during the summer to see how hot the players might be. But as long as that thermometer remains in the sun, it will continue recording a higher and higher temperature. The energy from the sun, the radiant energy, will make that liquid expand and expand.
In order to shade thermometers from the sun, special instrument shelters are used to house thermometers, as well as other weather instruments. The shelter is painted white to reflect the sun and has louvered sides so that air circulates through its interior. The housing is placed a standard five feet above a grassy surface. However, out of necessity, the shelter is often located on top of a building with other surfaces: tar, gravel, or concrete. The shelters also protect the instruments from rain and snow. Humidity instruments are normally placed in these shelters.
Anemometers are installed well above buildings and away from obstructions. Ideally, the instrument tries to indicate the wind as it flows freely above the surface. These instruments are placed about 10 meters, or 33 feet, above the surface.
Barometers can be placed conveniently indoors because the outdoor and indoor pressures should be the same, unless some dramatic changes are taking place, such as with an approaching tornado.
Excerpted from The Complete Idiot's Guide to Weather © 2002 by Mel Goldstein, Ph.D.. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.