Weather Instruments

  • Created by: Seancog
  • Created on: 13-05-17 15:37

Rain Gauge

A rain gauge is a cylinder which catches rainfall and has a funnel which directs the rain into a measuring flask. They are placed where they are not sheltered from the rain, and sometimes in a slight hole, to ensure it is not blown over. The reading is recorded daily, in millimetres.

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Measures air pressure. A glass tube about 1 metre tall is placed upside down in a container and contains a column of mercury with a vacuum at the top. When the pressure of the air is high, the weight of the air pushes up the level of the mercury in the glass tube and the reading on the glass tube is high. If the weight of mercury is greater than the air pressure, the mercury level falls. This is because the mercury in the glass tube can fall as the mercury can flow down into the container. 

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Wind Vane

A wind vane has a pointer/arrow that can spin around. The front of the pointer/arrow faces into the wind. Most wind vanes have the points of the compass below the pointer. They are usually located high up, where they are exposed to the wind.

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Measures wind speed. The cups on the anemometer catch the wind and spin around. The reading is displayed on the instrument in knots/mph, after a small computer has counted the number of revolutions, and has worked out the wind speed.. They are placed in the open, exposed to the wind. 

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Stevenson Screen

A box which holds weather instruments. Painted white to reflect heat. Sunlight doesn't affect readings Air can still flow through vents. Allows for consistent and accurate readings. Can be raised to prevent damage from people/animals. 

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Maximum-Minimum Thermometer

Made up of a U-tube, alcohol, a column of mercury and two metal indicators. When the temperature rises, the alcohol expands and moves down the left hand tube and so pushes the mercury up the right hand tube. This pushes the maximum indicator up the tube. The opposite happens when the temperature drops. The indicators will become stranded at the maximum and minimum temperatures. The readings are recorded every day, and a magnet is used to reset the indicators. The bottom of each marker should be read.

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