Measuring and recording weather data requires several pieces of equipment. Comprehensive world weather reporting requires measurements that follow the same guidelines, so weather-monitoring instruments are set up to follow the standards set by the World Meteorological Organization (WMO). These instruments range from the common thermometer to more obscure items that can measure light.
Temperature and Rain
Weather data relies on specialized versions of some basic instruments. Thermometers measure temperature, but they must be protected in order to get a correct reading. Placing them in the open can cause thermometers to overheat on hot days or freeze from precipitation in colder weather. The WMO requirement for the placement of the thermometer is about six feet above the ground. These thermometers usually sit inside a raised shelter, which can be a ventilated wooden box on stilts or a cylindrical case that looks like a series of upside-down plates stacked on top of each other. Rain gauges collect rainwater in order to measure how much rain has fallen. This measurement is taken by weighing the water or observing the gauge -- it depends on the model.
Humidity and Wind
Wind is measured using both wind vanes and anemometers. Wind vanes point out the direction the wind is blowing in, while anemometers rotate as the wind pushes a series of cups attached to a central spindle. A dial similar to a car's speedometer measures how fast the spindle is turning. Hygrometers measure humidity. They actually use hair as a component -- as the humidity increases, it causes dry, blond hair inside the hygrometer to expand in length. This is similar to the effect humidity has on the hair on your head.
Upper Atmosphere
Meteorologists use airplanes to monitor some weather phenomena. For example, planes are used by hurricane spotters, but they can only fly so high. An instrument called a radiosonde takes measurements at altitudes much higher than regular planes can go. NASA says that weather balloons can carry radiosondes 19 miles high, so they can monitor winds and other atmospheric conditions. In comparison, the 35,000-foot cruising altitude of passenger planes is only about 6 1/2 miles high.
Measuring Sunshine
It is possible to measure the amount of sunshine -- not just the heat, but the brightness of the light. An instrument called the Campbell-Stokes sunshine recorder, which looks like a combination of a microscope and a globe anchored in a half-moon frame, records how much bright sunshine a particular day has. A glass globe sits in a C-shaped frame, tilted diagonally, with a stylus connected to the bottom of the globe that points towards a piece of paper. An additional semicircular frame runs perpendicular to the first one, behind the globe. The globe amplifies sunlight to the point that the stylus burns the paper, leaving an elongated mark that denotes how many hours of bright sunlight occurred that day. This is measured in watts per square meter.
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