Weather Measurements and Instruments

Thermometer Thermometers measure air temperatures. (The average kinetic energy of air molecules). Thermometers work because matter expands when heated. Most thermometers are closed glass tubes containing liquids such as alcohol. Data is recorded in degrees Celsius(°C) or degrees Farenheig (°F)

Barometer A barometer measures air pressure. There are two types of Barometers: Mercury Barometer and Aneroid Barometer. Aneroid Barometers give data in Hectopascals (Hp—same as millibars mb. Standard pressure is 1013.25 Hp)

Barometer: How it works A Mercury Barometer consists of a glass tube inserted into a dish of mercury or colored denatured alcohol. *(If you build your own, don’t use mercury—it is poisonous)

Barometer: How it works The surrounding air presses down on the mercury in the dish and forces some of the mercury up into the tube. The height to which the mercury rises in the tube is directly proportional to the atmospheric pressure. Data is given in mm or in of Hg (760 mm or 29.92 in. is standard pressure)

Psychrometer A psychrometer measures the humidity of the air. One of the two thermometers has a wick (cloth cover) which is dipped in distilled water.

Psychrometer: How it works Evaporation of water from the wick on the wet bulb thermometer leads to cooling. Using a Relative Humidity Table, the temperature difference between the two thermometers gives the relative humidity of the air (in percent).

Relative Humidity Table: This is an example of the type of table you would use.

One such psychrometer is a Sling Psychrometer. Measurements are taken by whirling the psychrometer with the handle.

Anemometer An Anemometer measures the wind speed. The cups catch the winds, turning a dial attached to the instrument.

Wind Vane or Weather Vane * It is a tool for measuring wind direction (N, S, E, W) It spins on a rod and points in the direction from which the wind comes. Weather map symbol: blows from flag to ball

Rain Gauge Type of instrument used by meteorologists Used to gather and measure the amount of liquid precipitation over a set period of time Most rain gauges generally measure the precipitation in millimeters