BIOLOGY · Stage 8 · Chapter 8: Weather and Climate
Biology 8.1 What is weather? — Meteorological Factors and Measurements — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
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Lesson summary
8.1 What is weather? — Meteorological Factors and Measurements — Alhussan International Academy — Biology (Stages 7–9) notes: Define weather, name the factors that describe it, describe the instruments used to measure them and explain why forecasts matter.Weather = the mix of atm…
- Extreme weather
- Weather versus climate
- Temperature
- Precipitation
- Air pressure
- Cloud cover and sunshine hours
Section 1 of 6Weather
- Weather = the mix of atmospheric events taking place in a particular place at a particular time.
- It is what you see outsidesunny, rainy, windy or cold, and it can change within hours.
- Cause
- weather on the ground results from factors in the atmosphere.
- Changes in air pressure affect wind direction and strength.
- Humidity and air temperature affect how many clouds form and how much precipitation falls.
- Extreme weather
- some combinations of conditions cause thunderstorms, hurricane-force winds, heat waves or droughts.
- Weather versus climate
- weather is short-term, while climate is the average weather of a region over a long period, usually at least 30 years.
Section 2 of 6Factors that describe weather
- Temperature
- how hot or cold the air is, in degrees Celsius.
- Precipitation
- water falling from the sky as rain, snow, sleet or hail.
- Humidity
- the amount of water vapour in the air.
- Air pressure
- the force of the air above a place.
- Falling pressure usually brings clouds and rain, and high pressure brings clear, settled weather.
- Wind
- moving air, flowing from high to low pressure, described by speed and direction.
- Cloud cover and sunshine hours
- how much of the sky is covered and how long the Sun shines.
Section 3 of 6Why pressure systems bring different weather
- Low pressure
- warm air rises and cools, and water vapour condenses to form clouds, so rain is likely.
- High pressure
- cold air sinks and warms, so clouds evaporate and skies clear.
Section 4 of 6Measuring weather
| Factor | Instrument | Unit |
|---|---|---|
| Temperature | Thermometer (kept in shade) | °C |
| Rainfall | Rain gauge | mm |
| Wind speed | Anemometer | m/s or km/h |
| Wind direction | Wind vane | Compass point |
| Air pressure | Barometer | millibars or hPa |
| Sunshine | Sunshine recorder | hours |
| Humidity | Hygrometer | % relative humidity |
- Weather station
- instruments are placed away from buildings and trees.
- Thermometer box
- a white, ventilated box shades the thermometer so sunlight does not heat it directly and give a false reading.
Section 5 of 6Recording data
- Collect measurements at the same time each day and repeat them over several days.
- Display results in tables and line graphs, with the independent variable such as time on the x-axis.
- Local records
- a small weather station or a notebook can record very local weather and show patterns.
Section 6 of 6Forecasting and why it matters
- Data sources
- forecasters collect data from ground stations, weather balloons, ships and satellites and use computer models to predict the next days.
- Accuracy
- forecasts are less accurate further ahead because the atmosphere is a complex system in which small changes grow.
- Local weather
- it can be the same across a country but is often very local, and hills, mountains and lakes change how the atmosphere behaves.
- Users
- forecasts are important to farmers, sailors and food manufacturers, who need to plan ahead.
- Seeds must be planted when rain will water them.
- People buy more ice cream and cold drinks when it is hot.
- Wider effects
- weather also affects travel, health and energy supply.
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