Wind power - Box 1 Wind power gathers speed 1. Sponsored by The sun supplies the energy that gives rise to the wind by warming the air in the Earth's atmosphere.
Warm air is lighter, per unit volume, than cool air, because as it warms up it expands.
For this reason, warm air rises. Warm air over the equator rises and then spreads outwards towards the poles. In the meantime, the cooler air from nearer the poles rushes in to replace the warm air that has risen over the equator. In this way, air is circulated around the globe - the moving air is what we call wind. Patterns of air circulation Because of the rotation of the Earth, winds move in complicated patterns.