Simulation / illustration · Illustration of the average pattern, drawn over the live wind
Wind belts
Averaged over time, the Earth's winds form belts circling the planet. The labels show where they usually are; the moving streaks show what the wind is actually doing today, which is often messier.
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The engine at the equator
The Sun heats the equator most. Warm, moist air rises there, forming tall rain clouds in a calm, cloudy band called the doldrums, or Intertropical Convergence Zone. High up, the air flows towards the poles, cools and sinks again at about 30° north and south. Sinking air is dry, which is why many of the world's great deserts lie near 30°.
Trade winds, westerlies and polar easterlies
Near the ground the air flows back towards the equator as the trade winds, turned by the Earth's spin so they blow from the north-east north of the equator and from the south-east south of it. Between about 30° and 60° the prevailing winds blow from the west: the westerlies, which bring weather systems to Britain and Japan. Near the poles, cold dense air flows outwards as the polar easterlies.
The belts move with the seasons
The rain belt follows the Sun north in the northern summer and south in the northern winter, shifting more over land than over sea. In East and South Asia this shift helps drive the monsoon, which brings Taiwan its wet summer season.
Did you know?
Sailors called the calm belts near 30° the 'horse latitudes' and the calm equatorial belt the 'doldrums', because sailing ships could be stuck there for weeks without wind.