Collecting Weather Data | Geography for GCSE/IGCSE - Year 11 PDF Download

Weather Instruments

Stevenson screen

• This setup involves a wooden box elevated on four legs at a height of 121 cm to prevent heat absorption from the ground and maintain thermometer bulbs at a standardized height of 125 cm.
• The box is painted white to reflect sunlight, constructed from wood to prevent heat conduction, and its sides are slatted to facilitate air movement.
• The roof consists of a double layer of wood with airspace in between for insulation.
• Placing the station on a grass-covered surface helps reduce ground heat radiation.
• Regular readings should be taken at consistent times each day.
• Modern meteorological stations utilize automated digital instruments for data collection and transmission to the Meteorological Office's computers.
• Instruments Found Inside the Station:
  • The instruments housed inside include the Maximum-minimum thermometer (Six's thermometer) and the Wet and dry bulb thermometer (hygrometer).
• Instruments Found Outside the Station:
  • External instruments comprise the Rain gauge, Wind vane, and Anemometer.
• Station Layout Guidelines:
  • Barometers and barographs should be positioned away from strong air currents, direct sunlight, and heat sources.
  • Thermometers must be placed clear of heat-radiating structures.
  • Wind vanes and anemometers need to be situated in open areas, away from trees or buildings, and at a distance from the nearest obstacle equivalent to at least three times their height.
  • The rain gauge should be located in an open space, with a clearance from the nearest object double its height.

Wind Direction

• Wind direction is determined using a wind vane.
• It indicates the compass point from which the wind is blowing, such as south, north, or northeast.
• The measurement unit for wind direction is based on compass directions.

Wind Speed

• Wind speed is measured using an anemometer.
• The unit of measurement for wind speed can be meters per second (m/s) or kilometers per hour (km/hr).
• An anemometer typically consists of 3 or 4 cups fixed on rotating metal arms.
• The speed of cup rotation and the number of rotations recorded correspond to the wind's strength.
• Digital handheld anemometers display readings as the fan rotates, with some models directly transmitting data to apps and computers.
• Placing wind vanes and anemometers away from obstructions like buildings and trees is crucial to prevent interference with air movements.
• Buildings can create wind tunnels or disrupt airflow, impacting the accuracy of wind measurements.

Precipitation Measurement

• Precipitation Defined: Precipitation refers to any form of water, such as hail, mist, rain, sleet, or snow, that falls to the earth's surface.
• Unit of Measurement: The standard unit for measuring precipitation is millimeters (mm).
• Measuring Procedure:
  • A rain gauge is a tool utilized to measure the amount of precipitation.
  • Every day, at a consistent time, the collected water is transferred into a tapered measuring cylinder.
  • The measuring cylinder should be placed on a flat surface for accurate readings.
• Reading the Water Level:
  • The water level in the measuring cylinder is observed at eye level, aligning with the lowest point of the water's meniscus.
  • Meniscus refers to the curved surface of the water in the cylinder.
• Recording Measurements:
  • Measurements are documented daily; if the reading is too small to quantify, it is noted as 'trace'.

Temperature Measurement

• Unit of measurement can be Celsius (°C) or Fahrenheit (°F) depending on location
• Temperature is typically gauged using a thermometer or thermograph
• Shade temperature is preferred due to varying air temperature influenced by direct sunlight and cloud cover

Types of Thermometers

• Various thermometers are available; the Six's thermometer is a classic model featuring both maximum and minimum thermometers in a U-shaped design

Temperature Measurements

• Daily minimum and maximum temperatures are commonly recorded
• Average daily temperature is calculated
• The range of temperature over 24 hours, known as diurnal temperature range, is determined
• Mean monthly temperature is computed by averaging daily mean temperatures for a month
• The annual mean temperature is derived from the sum of monthly means divided by 12

Thermograph Functionality

• A thermograph contains a bimetallic strip that deforms with temperature changes
• These variations are translated by amplifying levers onto graph paper, showing a temperature curve
• A vertical movement of 1 mm corresponds to approximately 1°C change

You may need to calculate temperatures for various scenarios, such as weather events or experiments.

Humidity and Hygrometers

• Definition of Humidity: Humidity refers to the amount of water vapor present in a given volume of air.
• Using Hygrometers: Wet and dry bulb thermometers, known as hygrometers, are employed to measure relative humidity.
• Relative Humidity Explained: Relative humidity indicates the quantity of water vapor the air holds concerning the maximum it could contain at a specific temperature.
• Effect of Temperature: Warm air has a higher capacity to retain water vapor compared to cold air.
• Saturation Point: When air holds the maximum moisture possible, it is considered saturated.
• Process of Saturation: If air is unsaturated, water evaporates from the wet bulb, causing cooling and a lower temperature reading on the thermometer.
• Saturated Air: In saturated conditions, evaporation ceases, resulting in both thermometers displaying the same temperature.

Pressure

• Air has weight and applies force on the Earth's surface
• Sea level pressure stands at about 1.03 kg/cm²
• Pressure changes with altitude and temperature
• Measurement unit: millibars (mb)
• Isobars are lines connecting points of equal pressure on a map

Types of Barometers

• Mercury Barometer
• Aneroid Barometer
• Barograph

Mercury Barometer

• Consists of a hollow tube with air removed
• One end submerged in a pool of mercury
• Mercury rises due to atmospheric pressure
• Height of mercury column fluctuates with air pressure changes

Aneroid Barometer

• Contains a vacuumed, flexible metal chamber
• Equipped with a spring to counter pressure changes
• Operates using levers and a pointer on a scale

Barograph

• Provides continuous pressure readings over a week
• Traces pressure changes on a rotating cylinder
• Paper on the cylinder marked with 2-hour intervals