weather instruments

• Digital thermometers


  Contain an electric resistor (thermistor) which is temperature sensitive. As temperature rises, the thermistor becomes more conductive. A microcomputer pinpoints the temperature by measuring the conductivity and displays it on a screen.
• Digital thermometers


  • Can be programmed to record the highest and lowest temperatures over a period and display these separately
• Temperature varies depending on the type of surface or exposure to sunlight, so meteorologists have agreed to standardise the measuring of temperature to allow for comparison
• The shade temperature is the agreed correct measure
• Stevenson Screen


  A box that shades the instruments from direct sunlight and has slatted sides to allow free flow of air. It is painted white to reflect sunlight and located on open ground away from buildings.
• Rain gauge


  A cylinder that catches precipitation and funnels it into a measuring flask. It is located in an open area and sunk into the ground to avoid excessive evaporation and provide stability in windy conditions.
• Using a rain gauge

  Each day the flask is taken out and the amount of precipitation is recorded in millimetres (mm) by transferring the liquid into a small measuring cylinder
• Modern weather forecasts often show rainfall as a shadow superimposed onto a map, obtained from rainfall radar
• The Met Office tracks current rainfall and produces real-time digital rainfall maps of the UK
• Wind vane


  The top section is loose and moves with the wind, while the base is fixed and orientated to show the main eight points of the compass. The arrow points to the direction FROM which the wind is blowing.
• Anemometer


  Has three cups mounted on a high pole to catch the wind. As the wind blows, the cups spin and the wind speed is recorded on a dial.
• Wind speed


  Measured in knots or km/h
• Wind


  Movements of air from high to low pressure
• Mercury barometer


  Composed of a glass tube about 1 m tall with one end open and the other end sealed, filled with mercury. The mercury level in the glass tube falls, creating a vacuum at the top. The barometer works by balancing the weight of mercury in the glass tube against atmospheric pressure.
• Aneroid barometer


  Operated by a metal cell containing a small amount of air. Increased air pressure causes the sides of the cell to come closer together, which is connected to a rotating pointer that moves over a scale on the face of the instrument.
• Types of clouds


  • Cirrus (high, wispy, made of ice crystals)
  • Cumulus (low, cotton wool-like, can develop into cumulonimbus)
  • Stratus (light grey, sheet-like)
• Nimbus


  Any cloud that is rain-bearing, indicated by its grey colour
• Geostationary satellites


  Hover over the same spot on the Earth, moving at the speed of the Earth's rotation, at an altitude of 36,000 km
• Polar satellites


  Pass around the Earth from pole to pole at a height of 850 km, providing daily global coverage
• Weather buoys


  Stationed in mid-ocean locations, transmitting weather data via satellite to weather centres for use in forecasting and climate study
• Weather ships

  Record and send weather data in the same way as buoys
• Rainfall radar


  Transmits harmless microwaves, which are scattered back by rainfall, allowing a rainfall image for a large area to be created