Weather InstrumentsWeather Instruments

ThermometerThermometer

What does it do?What does it do?

It measures the It measures the air temperatureair temperature

How do they work?How do they work?

Most thermometers are closed glass Most thermometers are closed glass tubes containing liquids such as tubes containing liquids such as alcohol or alcohol or mercury. mercury.

When air around the tubeWhen air around the tube heats the heats the liquid, liquid, the liquid expands and moves the liquid expands and moves up the tube.up the tube.

BarometerBarometer

What does it do?What does it do?

It measures It measures air pressureair pressure

How does it work?How does it work? It tells you whether or not the air It tells you whether or not the air

pressure is pressure is risingrising or or falling.falling.

When a barometer reading is rising, When a barometer reading is rising, it means sunny and dry.it means sunny and dry.

When a barometer reading is falling, When a barometer reading is falling, it means stormy weather is coming! it means stormy weather is coming!

The first barometer was built in 1643 The first barometer was built in 1643 by an Italian scientist named by an Italian scientist named Torricelli.Torricelli.

It works by balancing the weight of It works by balancing the weight of mercurymercury in the glass tube inside in the glass tube inside against the atmospheric pressure, against the atmospheric pressure, just like a set of scales.just like a set of scales.

If the weight of mercury is If the weight of mercury is lessless than than the atmospheric pressure, the the atmospheric pressure, the mercury level in the glass tube mercury level in the glass tube risesrises..

If the weight of mercury is If the weight of mercury is moremore than than the atmospheric pressure, the the atmospheric pressure, the mercury level mercury level falls.falls.

Sling PsychrometerSling Psychrometer

What does it do?What does it do?

It measures It measures relative humidityrelative humidity, using , using the cooling effect of the cooling effect of evaporationevaporation..

How does it work?How does it work?

Two thermometers are used.Two thermometers are used. A wet cloth is placed on one of the two A wet cloth is placed on one of the two

thermometers in the psychrometer. The thermometers in the psychrometer. The psychrometer is psychrometer is swungswung around a few around a few times. times.

Water Water evaporates from the clothevaporates from the cloth, causing , causing the temperature on that thermometer to the temperature on that thermometer to be lower than the other. Then you can be lower than the other. Then you can calculate the relative humidity – calculate the relative humidity – comparing one thermometer to the other.comparing one thermometer to the other.

Rain GaugeRain Gauge Measures Measures the amount of rain that has the amount of rain that has

fallen over a specific period of time.fallen over a specific period of time.

Wind VaneWind Vane

Determines the Determines the directiondirection from which from which the wind is blowing.the wind is blowing.

AnemometerAnemometer

Measures Measures wind speedwind speed..

HygrometerHygrometer

Measures the water vapor content of Measures the water vapor content of the air, or the the air, or the humidity.humidity.

Weather BalloonWeather Balloon

A WEATHER BALLOON measures A WEATHER BALLOON measures weather conditionsweather conditions higher up in the higher up in the atmosphere. atmosphere.

Weather SatellitesWeather SatellitesUsed to track and Used to track and photographphotograph large large

weather systems.weather systems.