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 intothe glass tube.

• Measurement unit: hPa (hectoPascals) or mm

http://www.ludolph.de/Handel%20Barometer%20262238.jpeg

www.usatoday.com/weather/wbaromtr.htm

http://geography.sierra.cc.ca.us/booth/Physical/chp5_atm_pressure/barometer.gif

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)

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