Weather InstrumentsWeather Instruments

GeographyGeography

TemperatureTemperature• Max Min Thermometer• Six’s Thermometer

– Max-Mercury– Min-Alcohol

• Measures shade temperature (Stevenson’s screen)

• Read off at bottom of the index (reset with magnet)

• Read at eye level• Measured in ºC

HumidityHumidity

• Wet/Dry Bulb thermometer• Hygrometer

– Wick and reservoir of water

• Comparison tables1. Calculate depression of wet

bulb (Dry – Wet)2. Read off table

• Measures in shade (Stevenson’s screen)

• Units = % Relative humidity

Wind SpeedWind Speed

• Anemometer– Cups or blades

– Clear unobstructed location

• Km per hour

Wind DirectionWind Direction

• Wind Vane• Recorded on Wind Rose

• Compass Directions

Air PressureAir Pressure• Aneoid Barometer

• Barograph– Plots changes in pressure

• Millibars• Measured in shade

(Stevenson’s screen)

RainfallRainfall

• Rain gauge

• Siting factors– Clear view of sky– Recessed into ground– Approx 30cm above

ground– Grassy surface (avoid

splash back)– Read off at eye level

• Regular intervals (24hours)

SunshineSunshine

• Sunshine recorder– Burns a timeline– Traces sun shine not

hours of daylight

• Glass ball focuses light

• Burns line onto card

• Units = Hours

Stevenson’s ScreenStevenson’s Screen

• Houses temperature / humidity /pressure instruments

• Features– Insulated roof– Painted white to reflect

heat– Louvered (slatted)

sides aid air circulation– Located 1.25-2m

above ground

Cloud CoverCloud Cover

• Cloud Mirror• Divide mirror into 16

equal squares• Lay mirror on ground

with clear view of sky• Estimate cover

• Units = Oktas