World Wind Belts — free printable diagram

The global wind belts

The Earth's prevailing winds are not random: they fall into bands that circle the planet, because the sun heats the equator far more strongly than the poles. Warm air rises at the equator, travels polewards high up, sinks again around 30° north and south, and returns — three such loops in each hemisphere, and the surface part of each loop is a wind belt.

Trade winds

0°–30° — blow towards the equator, from the north-east and south-east

Westerlies

30°–60° — blow from the west

Polar easterlies

60°–90° — blow from the east

The three cells

Hadley, Ferrel and Polar, in each hemisphere

Rising air

At the equator and around 60° — low pressure, wetter

Sinking air

Around 30° and at the poles — high pressure, drier

What deflects the winds

The Coriolis effect, caused by the Earth's rotation

• Winds are named for the direction they come from, not the direction they are heading. A westerly blows from the west towards the east — the single most common error in reading this diagram.
• The belt of sinking air at about 30° north and south is why the world's great hot deserts sit in two bands at those latitudes: descending air warms and dries, so little rain falls.
• Rising air at the equator does the opposite, which is why the equatorial belt is the wettest part of the planet and where tropical rainforest is found.
• Without the Earth's rotation the winds would blow straight north and south between the pressure belts. The Coriolis effect deflects them — to the right in the northern hemisphere and to the left in the southern — which is what turns them into easterlies and westerlies.
• The trade winds got their name from sailing ships, which relied on their steadiness to cross the Atlantic; the westerlies were the reliable return route further north.
• The whole pattern shifts north and south through the year as the overhead sun moves between the tropics, which is what gives places on the edge of a belt a distinct wet and dry season.