Instruments used for measuring weather elements

A variety of instruments are employed to measure different aspects of weather, such as temperature, rainfall, humidity, sunshine, pressure, wind speed, and direction. Each tool is designed for precision and is placed in specific conditions to ensure accurate readings.

Tools for weather measurement

• Stevenson screen:
  • A wooden box elevated about 1.2 metres above the ground on four legs, featuring slatted sides for air circulation and a double-boarded roof.
  • Painted white to reflect sunlight, it is placed on a grassy surface to minimise ground heat interference.
  • It houses thermometers for temperature and humidity readings.
• Rain gauge:
  • A cylindrical device with a collecting can containing a glass or plastic jar, topped with a funnel to direct rainwater into the container.
  • It needs to be checked daily at a consistent time and typically includes a measuring cylinder marked up to 100 mm.
• Maximum-minimum thermometer:
  • Used to record the highest and lowest temperatures over a day.
  • The maximum part uses mercury, which expands with heat and moves an index to the highest temperature reached.
  • The minimum part uses alcohol, which contracts in cold, pulling an index to the lowest point.
  • Mean daily temperature = (maximum + minimum) ÷ 2
• Wet- and dry-bulb thermometer (hygrometer):
  • Measures relative humidity.
  • The dry-bulb records the actual air temperature, while the wet-bulb, wrapped in a water-soaked muslin bag, shows a lower temperature due to evaporation unless humidity is near 100%.
• Sunshine recorder:
  • Tracks the duration of sunshine in hours and minutes.
  • The Campbell-Stokes model uses a glass sphere to focus sunlight, creating burn marks on a recording sheet to indicate sunshine periods.
• Barometer:
  • Measures atmospheric pressure using a mercury-filled tube with air removed.
  • The height of the mercury column fluctuates with changes in air pressure, rising as pressure increases.
• Anemometer:
  • Determines wind speed through rotating cups on a vertical shaft.
  • The speed of rotation corresponds to wind strength, recorded in kilometres per hour (km/h).
• Wind vane:
  • Shows wind direction with a horizontal rotating arm.
  • The pointer faces into the wind, with fixed markers indicating cardinal directions (north, south, east, west).

Digital instruments offer precise and less subjective readings compared to traditional tools.

Methods for recording and classifying weather data

Recording weather data involves systematic observation and classification of atmospheric conditions like cloud types and cover.

Techniques for weather data recording

• Cloud Classification - Clouds are categorised by altitude and composition:
  • High clouds (5,500-14,000 m) - Made of ice crystals, including cirrus, cirrostratus, and cirrocumulus.
  • Medium clouds (2,000-7,000 m) - Composed of water droplets or a mix with ice crystals, such as altostratus and altocumulus.
  • Low clouds (below 2,000 m) - Mainly water droplets, including stratus, stratocumulus, and nimbostratus.
  • Clouds with vertical development - Encompass cumulus and cumulonimbus, the latter containing ice crystals.
• Cloud Cover Measurement - Assessed visually in oktas, which divide the sky into eighths. A measurement of 8/8 oktas means the sky is fully covered by clouds.
• Climate graphs (climographs):
  • Visual tools that illustrate temperature and rainfall trends.
  • Temperature is represented as a line graph, while rainfall is shown as a bar chart.
  • The mean monthly temperature is calculated as an average between the monthly maximum and minimum values, with separate scales used for temperature and precipitation.

Interpreting climate graphs for weather patterns

Climate graphs, also known as climographs, combine temperature and rainfall data to provide a comprehensive overview of climatic conditions.

Components of climate graphs

• Temperature Line - Plotted as a continuous line graph, showing monthly average temperatures.
• Rainfall Bars - Displayed as vertical bars, representing the total monthly precipitation.
• Scales - Separate scales for temperature (usually on the left) and rainfall (on the right) to accommodate different units and ranges.
• Mean Monthly Temperature - Derived from averaging the monthly maximum and minimum temperatures, providing a midpoint for analysis.