Wind power gathers speed

Box 1 | What causes the wind?

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.

But the atmosphere is warmed unevenly by the sun: the poles, for example, are cold while the equator is hot. 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. In northern Australia the winds blow mostly from the east, while in southern Australia they blow mostly from the west. On top of this general circulation pattern we find other winds associated with tropical cyclones in northern Australia or with cold fronts in the south.

All winds blow in circles. The major circulation patterns of easterly winds or westerly winds blow right around the Earth, carrying weather patterns with them. Local winds, as in cyclones or other low-pressure systems, blow in circles clockwise around the centre or eye of the storm.

Predicting windy sites

Other factors also have a profound influence on the nature of atmospheric circulation and wind patterns. These include the location of the continents, the season, and topographic features such as mountain ranges, valleys and ridgelines. This means that predicting the best areas for electricity generation from wind power can be quite complex. Scientists use computer models and extensive wind measurements to assist in this.

Boxes
Box 2. The environmental credentials of wind power
Box 3. Energy basics
Box 4. The power of the winds

Related sites
Forces acting to create wind (PhysicalGeography.net, Canada)
Wind-power: Where's the best site for a wind generator? (CSIRO Land and Water, Australia)

External sites are not endorsed by the Australian Academy of Science.
Posted August 1998.