Meteorologist use various weather instruments and gauges to make measurements. Thermometers measure temperature, humidity is measured by a hydrometer, a barometer detects atmospheric pressure, an anemometer measures wind speed and gauges measure rain and snow.
Thermometer – Mercury Rising
Thermometers measure air temperature. More specifically, this device measures the air’s heat content. The idea of “mercury rises” actually refers to traditional thermometers, which use liquid to generate readings. Heat causes the liquid within the thermometer to expand and travel up and down the tube. Temperatures are measured in degrees Celsius or degrees Fahrenheit, depending on location.
Official thermometers used for keeping weather records, measure the temperature about 5 feet above the ground, usually within a specified shelter. This is important because wind and environmental effects, such as topography, or shade and shadows, can skew thermometer readings.
Hydrometer
A hydrometer or hygrometer measures humidity or the amount of water vapor in the air. Another simple explanation of humidity is that it is a measure of comfort at different temperatures. More humidity, like in some regions east of the Rockies, equals more discomfort.
Relative humidity is another way to express how the temperature feels. In the same way, relative humidity calculates the amount of moisture in the air. Relative humidity refers to the saturation point of water vapor in the air. Relative humidity value “is the amount as a percentage of that required to saturate the air completely” (BBC, 2008).
Barometer
A barometer measures air pressure. This instrument weighs the amount of air in a specific place. A barometer can be considered a weather predictor, rising and falling with advancing storms. A falling barometer indicates an advancing storm or bad weather. A rising barometer indicates improving weather. An aneroid barometer is the most basic way to measure air pressure. This device simply measures the “expansion and contraction of an airless metal box as air pressure changes” (BBC, 2008).
Anemometer
This weather instrument measures wind speed or velocity. In order words, an anemometer measures the strength of the air’s motion. Official readings of wind speed are measured at 33 feet above the ground on buildings or airports. The typical anemometer used to make measurements is a cup anemometer. Several cups catch the wind, spinning them around a vertical pole. Wind speed is calculated by the number of revolutions per minute.
Windsocks, which measure direction and strength of the wind, are also used at airports, easily visible to pilots and airport crew. A weather vane measures wind direction, using arrows to point out the direction of motion.
Rain or Snow Gauge
Precipitation is measured in a rain gauge or snow gauge. Rain gauges can be any container, with marked measurements of inches, centimeters or millimeters. It is important to use the correct rain gauge, as evaporation can be a factor. Calculating snow depth can be tricky. A simple calculation used is 10 inches of snow is roughly equivalent to 1 inch of rain or water.
Sources:
BBC
Cox, John D. Weather for Dummies. 2000. Wiley Publishing Inc, Hoboken, New Jersey.
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