Global atmospheric circulation: AQA GCSE Geography revision notes

Global atmospheric circulation

Why the air moves

The sun heats the Earth unevenly: most strongly at the equator, least at the poles. The atmosphere moves heat from the equator towards the poles.

Where air is heated, it rises, leaving at the surface. Where air cools, it sinks, creating . Winds blow along the surface from high pressure to low pressure.

The Earth's spin bends winds sideways, so they blow at an angle rather than straight from north to south. This is the .

Key terms

The three cells

In each hemisphere, air circulates in three loops, or cells:

(0°–30°): air rises at the equator, flows towards the poles high up, sinks at 30° and returns towards the equator along the surface.
(30°–60°): air sinks at 30°, flows towards the poles along the surface and rises at 60°.
(60°–90°): air rises at 60°, flows to the pole, sinks there and returns along the surface.

Remember

Rising air at 0° and 60° means low pressure; sinking air at 30° and 90° means high pressure.

Key terms

Pressure belts, winds and climate

Latitude	Pressure	Surface winds	Climate it helps explain
0° (equator)	Low	Trade winds meet	Hot and wet all year: tropical rainforests
30°	High	Trade winds blow towards the equator; westerlies towards the poles	Dry, clear skies: hot deserts
60°	Low	Westerlies meet the polar easterlies	Unsettled and wet: the UK
90° (poles)	High	Polar easterlies	Cold and dry

The bring the UK its mild, wet weather from the Atlantic.

Exam tip

Link the pattern to places: rising air at the equator explains rainforests; sinking air at 30° explains deserts such as the Sahara.

Key terms

Exam practice

Plan your own answer first, then open the model answers to see what each level looks like.

6 marks · about 6 minutes

Explain how the global atmospheric circulation affects the weather and climate of different places.

Explain means: Give the reasons why something happens, developing each point with "because" or "so".

Level 1 (Basic)· 2/6 marks (band 1–2)

At the equator it is hot and wet because the sun is strong. Deserts are at 30° and are dry. The UK is wet.

Why this level: Correct descriptions of weather in places, but no explanation of how the circulation causes them. To reach Level 2: explain where air rises and sinks, and what that does to pressure and rainfall.

Level 2 (Clear)· 4/6 marks (band 3–4)

At the equator, the sun heats the ground strongly, so air rises, creating low pressure. As it rises it cools and forms clouds, giving heavy rain, so rainforests grow there. At about 30° north and south, the air sinks, creating high pressure and dry, clear skies, so there are hot deserts.

Why this level: A clear explanation of two places, linking rising and sinking air to pressure and rainfall. To reach Level 3: cover more of the system, such as 60° and the UK, and the surface winds.

Level 3 (Detailed)· 6/6 marks (band 5–6)

The Earth is heated unevenly, so air rises in some places and sinks in others. At the equator, strong heating makes air rise, giving low pressure; it cools and condenses, bringing heavy daily rain, so rainforests grow there. The air then flows towards the poles and sinks at about 30°, giving high pressure and clear, dry skies, which is why the Sahara and other hot deserts lie there. At about 60°, warm westerly winds meet cold polar air and rise, giving low pressure. This is why the UK has frequent depressions and unsettled, wet weather. Surface winds, such as the trade winds blowing back to the equator, complete the cells.

Why this level: A detailed, linked explanation of the whole system, from heating to pressure to rainfall, with named places (Sahara, the UK). This is Level 3.

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