Weather, Climate and Ecosystems » Elements of weather and measurement

What you'll learn this session

Study time: 30 minutes

The seven key elements of weather (temperature, precipitation, humidity, air pressure, wind, cloud cover, sunshine)
How to measure each element using appropriate instruments
How to read and interpret weather data
The difference between weather and climate
How weather measurements contribute to climate studies

Elements of Weather and Their Measurement

Weather affects our daily lives in countless ways - from what clothes we wear to whether school sports day goes ahead! Understanding how to measure weather helps us predict what might happen next and understand long-term climate patterns.

Key Definitions:

Weather: The day-to-day conditions of the atmosphere in a particular place, including temperature, rainfall, wind, etc.
Climate: The average weather conditions in a place over a long period (usually 30+ years).
Meteorology: The scientific study of the atmosphere and weather patterns.

The Seven Elements of Weather

Weather is made up of seven main elements that can be measured and recorded. Let's explore each one!

🌡 Temperature

What is it? Temperature measures how hot or cold the air is. It's caused by the sun's radiation heating the Earth's surface, which then heats the air above it.

How we measure it: Using a thermometer, which can be:

Traditional liquid-in-glass thermometer (mercury or alcohol)
Digital thermometer
Maximum-minimum thermometer (records highest and lowest temperatures)

Units: Degrees Celsius (°C) or Degrees Fahrenheit (°F)

Fun fact: Temperatures are always measured in a Stevenson Screen - a white box with slats that protects instruments from direct sunlight and rain while allowing air to flow freely.

🌧 Precipitation

What is it? Any form of water falling from the sky - rain, snow, sleet, hail, etc.

How we measure it: Using a rain gauge - a simple container that collects rainfall over a set period.

Standard rain gauge: A cylinder with a funnel top
Tipping bucket rain gauge: Automatically records rainfall intensity
Snow is measured using a snow gauge or by melting collected snow

Units: Millimetres (mm) or inches (in)

Key point: 1mm of rainfall means 1 litre of water has fallen on each square metre of ground.

💧 Humidity

What is it? The amount of water vapour in the air.

Types:

Absolute humidity: The actual amount of water vapour in the air
Relative humidity: The percentage of water vapour in the air compared to the maximum it could hold at that temperature

How we measure it: Using a hygrometer

Wet and dry bulb thermometer (psychrometer)
Hair hygrometer (human hair stretches with humidity)
Electronic hygrometer

Units: Relative humidity is measured as a percentage (%)

Why it matters: High humidity makes hot days feel even hotter because sweat can't evaporate easily from our skin.

⚖ Air Pressure

What is it? The weight of air pressing down on the Earth's surface.

How we measure it: Using a barometer

Mercury barometer: A glass tube with mercury that rises or falls with pressure changes
Aneroid barometer: Uses a metal box that expands and contracts
Digital barometer: Electronic sensor

Units: Millibars (mb) or hectopascals (hPa)

Weather prediction:

Falling pressure often means rain or storms approaching
Rising pressure typically indicates fair weather
Standard pressure at sea level is 1013.25 mb

🌬 Wind

What is it? Air moving from high to low pressure areas.

How we measure it:

Speed: Anemometer (cups that spin faster in stronger winds)
Direction: Wind vane (points to where wind is coming from)

Units: Kilometres per hour (km/h), miles per hour (mph), knots, or Beaufort scale (0-12)

Remember: Wind is named by the direction it comes FROM, not where it's going!

☁ Cloud Cover

What is it? The fraction of the sky covered by clouds.

How we measure it:

Visual observation (traditional)
Measured in oktas (eighths of the sky)
Modern weather stations use ceilometers (laser devices)

Units: Oktas (0 = clear sky, 8 = completely overcast)

Cloud types: Cirrus (high), Cumulus (fluffy), Stratus (layered), Nimbus (rain-bearing)

☀ Sunshine

What is it? The duration of bright sunshine.

How we measure it:

Campbell-Stokes recorder (glass sphere that burns a card as the sun moves)
Electronic sunshine recorders

Units: Hours and minutes per day

Importance: Affects plant growth, solar energy production and tourism

Weather Stations and Data Collection

Weather stations are places where weather elements are regularly measured and recorded. They range from simple school weather stations to sophisticated automated systems used by meteorological services.

Case Study Focus: Stevenson Screen

The Stevenson Screen is a vital part of any weather station. Invented by Thomas Stevenson (father of author Robert Louis Stevenson) in the 1860s, it's a white wooden box with louvred sides that:

Shields instruments from direct sunlight and radiation
Protects from rain and snow
Allows free air movement around the instruments
Is painted white to reflect heat
Is positioned 1.25m above ground level
Contains thermometers and sometimes a hygrometer

This standardised housing ensures that temperature readings from around the world can be accurately compared.

Recording and Interpreting Weather Data

Weather data is collected at regular intervals (typically hourly) and recorded in a systematic way. This data can then be used to:

Create weather forecasts
Identify weather patterns
Contribute to climate records
Help with planning in agriculture, construction and other industries

Reading Weather Instruments

When taking readings from weather instruments, it's important to:

Take readings at the same time each day for consistency
Record data immediately to avoid forgetting
Ensure instruments are properly maintained and calibrated
Follow standard procedures for each measurement

📈 Weather Graphs and Charts

Weather data is often presented visually using:

Line graphs: Show changes over time (e.g., temperature throughout a day)
Bar charts: Good for showing rainfall totals
Wind roses: Show wind direction frequency and strength
Synoptic charts: Weather maps showing pressure systems, fronts and other features

Being able to read these charts is an essential skill for understanding weather forecasts and patterns.

Weather vs Climate: Understanding the Difference

While weather and climate are related, they describe different aspects of atmospheric conditions:

⛅ Weather

Definition: The state of the atmosphere at a particular place and time

Timeframe: Short-term (minutes to days)

Example: "It's raining in London today" or "We had a frost last night"

Measurement: Specific values (e.g., 25°C, 10mm of rain)

🌍 Climate

Definition: The average weather pattern in a place over many years

Timeframe: Long-term (30+ years)

Example: "The UK has a temperate maritime climate" or "The Sahara has an arid climate"

Measurement: Statistical averages and ranges (e.g., average annual rainfall)

Weather measurements, when collected over many years, form the basis of our understanding of climate. This is why consistent, accurate weather recording is so important for climate science.

Practical Activity: Create Your Own Weather Station

You can make simple weather instruments at home or school:

Rain gauge: Use a clear plastic bottle with straight sides. Cut off the top, invert it to make a funnel and mark measurements on the side.
Wind vane: Attach an arrow cut from cardboard to a pencil with a pin and mount it so it can rotate freely.
Barometer: Stretch a balloon over a jar mouth, attach a straw to the centre with tape and watch it rise or fall with pressure changes.

Keep a weather diary for a month, recording your measurements at the same time each day. Can you spot any patterns or make predictions?

The Importance of Weather Measurement

Accurate weather measurement is crucial for:

Weather forecasting and severe weather warnings
Agriculture and food production
Aviation and shipping safety
Urban planning and building design
Energy demand prediction
Climate change research
Historical records and understanding past climate

Modern weather measurement has become increasingly sophisticated, with automated weather stations, weather satellites, weather radar and computer modelling all playing important roles in how we understand and predict weather patterns.