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Weather Instruments for Geography Revision

Apr 25, 2025

Weather Instruments IGCSE Geography - Revision Notes

Stevenson Screen

  • Wooden box on four legs at 121 cm height to avoid ground heat.
  • Painted white to reflect sun’s rays.
  • Made of wood to prevent heat transfer; sides slatted for air movement.
  • Double-layered wood with airspace for insulation, placed on grass.
  • Contains:
    • Maximum-minimum thermometer (Six’s thermometer)
    • Hygrometer with wet and dry bulb
  • Instruments outside include rain gauge, wind vane, and anemometer.
  • Weather station layout avoids heat sources, severe winds, and direct sun.

Wind Measurement

Wind Direction

  • Measured with a wind vane.
  • Direction is the compass point from where the wind blows.

Wind Speed

  • Measured with anemometers in m/s or km/hr.
  • Anemometers have cups that rotate to measure wind speed.
  • Digital anemometers send data to apps/computers.

Precipitation

  • Measured using a rain gauge in millimeters (mm).
  • Collected water poured into a measuring cylinder daily.
  • Eye-level reading of the water’s meniscus is recorded.

Temperature

  • Measured in Celsius or Fahrenheit.
  • Instruments include thermometers or thermographs.
  • Traditional Six’s thermometer measures daily min/max temperatures and calculates averages.
  • Diurnal temperature range and mean monthly/annual temperatures can be calculated.

Humidity

  • Measured with hygrometers using wet and dry bulb thermometers.
  • Relative humidity compared to air’s maximum capacity at a given temperature.

Air Pressure

  • Measured in millibars (mb) using a barometer.
  • Types:
    • Mercury barometer
    • Aneroid barometer
    • Barograph
  • Pressure readings shown by changes in mercury or using levers for aneroid/barograph.

Sunshine

  • Measured with a Campbell-Stokes sphere.
  • Sunlight scorches a card, indicating sunshine duration.
  • Positioning: open area, south-facing in the northern hemisphere.

Cloud Cover

  • Measured in oktas (eighths of the sky covered by clouds).
  • Different cloud types based on shape and height (e.g., cirrus, stratus, cumulus).

Tropical Storms

  • Known as typhoons, hurricanes, or cyclones based on location.
  • Rated on Saffir-Simpson scale, categories 1-5 based on wind speeds.
  • Category 3 and above is considered major.
  • Feature intense low-pressure systems with a central eye.