Weather Measurement Tools

Thermometer What? –Measures the air temperature How? –Heat expands the liquid in the vacuum tube and causes it to “rise”, likewise, cold causes the liquid in the vacuum tube to contract. Measurement unit: degrees Celsius (°C) Fun Fact: Thermometers were refined for studying weather, not for any other science.

Psychrometer What? –Measures humidity in the air – relative humidity How? –By comparing the temperature of a “dry bulb” thermometer with that of a “wet bulb” thermometer. –When water evaporates from the cloth it absorbs heat and produces a cooling effect on the wet bulb thermometer. –If the humidity is low, more evaporation will occur causing more cooling and a lower temperature on the wet bulb thermometer. If the humidity is high, not much evaporation will take place causing less cooling and not as great of a difference between the wet and dry bulb readings. The wet bulb thermometer will most always have the lower temperature. Measurement Unit: percent (%)

Barometer. What? –Measures atmospheric pressure How? –The drawing shows the basic principles of a barometer. –A glass tube from which the air has been removed is inserted into a dish of mercury. The air pressing down on the mercury in the dish forces some of the mercury up into the glass tube. Measurement unit: hPa (hectoPascals) or mm

Anemometer What? –Measures wind speed How? –By counting the number of revolutions in a set amount of time. (Calibration required) Measurement unit: usually kilometers per hour (km/h)