Weather Revision Notes

Weather data collection involves measuring atmospheric conditions such as temperature, pressure, humidity, wind, precipitation, and sunlight. Data can be gathered manually by observers or automatically using weather stations equipped with digital sensors. Accurate data collection requires proper instrument placement and regular observation schedules.

Manual methods include reading instruments housed in protective shelters and recording cloud observations. Automated stations provide continuous, real-time data, improving the precision and frequency of measurements.

Cloud observations involve identifying cloud types and estimating their coverage in oktas (eighths of the sky dome), which helps in understanding weather patterns and forecasting.

• Manual and automated methods complement each other in weather data collection.
• Regular observations ensure data reliability.
• Cloud type and amount are key qualitative data for weather analysis.

Each weather instrument is designed to measure a specific atmospheric variable. Correct placement is crucial to avoid errors caused by environmental factors.

The Stevenson Screen is a ventilated white box that houses thermometers, shielding them from direct sunlight and precipitation to ensure accurate air temperature readings. It is placed about 1.25 to 2 metres above ground on a grassy surface away from buildings and trees.

A rain gauge collects and measures precipitation. It is a cylindrical container with a funnel leading to a measuring tube, placed in an open area to avoid obstruction by nearby objects that could block rainfall or cause splashing errors. Measurements are usually recorded in millimetres, representing the depth of rainfall if spread evenly over the ground surface. For example, 10 mm of rain means 10 litres of water per square metre of ground area.

• Stevenson Screen protects thermometers from direct heat and moisture.
• Rain gauge placement must avoid obstructions to ensure accurate rainfall measurement.
• Height and surface type affect temperature readings.

The maximum-minimum thermometer records the highest and lowest temperatures over a period, typically 24 hours. It uses two mercury or alcohol columns and a marker to indicate extremes, allowing assessment of daily temperature range.

The wet-and-dry bulb thermometer, or hygrometer, measures humidity. The dry bulb records air temperature, while the wet bulb has a moistened wick; evaporation cools it, and the temperature difference between bulbs is used to calculate relative humidity using psychrometric tables or formulas.

A sunshine recorder measures the duration of bright sunshine, often using a glass sphere that focuses sunlight onto a calibrated card, burning a trace that indicates sunshine hours. It must be placed in an open area free from shade throughout the day to ensure accuracy.

• Maximum-minimum thermometer tracks temperature extremes for daily range.
• Wet-and-dry bulb thermometers provide humidity data through temperature differences.
• Sunshine recorders require unobstructed placement for valid sunshine duration.

The barometer measures atmospheric pressure, essential for weather forecasting. Mercury barometers use a column of mercury whose height changes with pressure; aneroid barometers use a sealed metal chamber that expands or contracts. Barometers are placed indoors away from heat sources to avoid false readings.

An anemometer measures wind speed, typically using rotating cups or propellers. It is mounted at a standard height (usually 10 metres) above ground in an open area to avoid turbulence caused by buildings or trees.

A wind vane indicates wind direction by pointing into the wind. It is installed alongside the anemometer at the same height and location to provide consistent wind data.

• Barometers must be shielded from heat to measure true atmospheric pressure.
• Anemometers and wind vanes require open, elevated placement for accurate wind data.
• Wind speed and direction are critical for understanding weather systems.

Cloud observation involves identifying cloud types such as cumulus, stratus, cirrus, and nimbus, each indicating different weather conditions. Observers estimate cloud cover in oktas, from 0 (clear sky) to 8 (completely overcast). For example, 4 oktas means half the sky is covered by clouds.

Calculations with weather data include determining temperature range by subtracting minimum from maximum temperature, calculating relative humidity from wet and dry bulb readings using psychrometric charts or formulas, and converting rainfall depth into volume over a given area.

Example calculation: If maximum temperature is 25°C and minimum is 15°C, temperature range = 25°C - 15°C = 10°C. This range helps understand daily temperature variability, which affects local weather conditions and human comfort.

• Cloud type and amount provide qualitative weather indicators.
• Temperature range is calculated by max minus min temperature.
• Relative humidity requires wet and dry bulb temperature difference and psychrometric data.

Weather data is often presented in graphs such as temperature line graphs, bar charts for rainfall, and wind roses showing wind speed and direction frequency. Understanding these visual tools allows analysis of patterns and trends.

For example, a climograph combines temperature and rainfall data over months to illustrate climate characteristics of a location. Recognising seasonal variations and extremes helps in predicting weather and planning activities.

Diagrams may also show pressure systems, fronts, and cloud cover, aiding in comprehensive weather interpretation. Accurate reading of these visuals requires familiarity with scales, units, and symbols used.

• Graphs reveal temporal patterns in weather variables.
• Climographs integrate temperature and rainfall for climate overview.
• Symbols and scales must be understood for correct diagram interpretation.