Nicholas Tangata, of King's High School, asks :-

Jon Deaker, of King's High School, asked:- Helena Johnson, of Manawatu College, asked:-

How is wind produced?

Keith Dawber, a physicist studying wind energy at the University of Otago, responded.

Wind is motion of the atmosphere and is driven by the effects of different densities of air at different places. The different densities are caused by an uneven distribution of heating and cooling over the surface of the earth including that of the land masses, the oceans and the polar ice caps.

Heating by the sun causes air to expand and become less dense, so that in the earth's gravitational field it becomes lighter and tends to float over the top of colder more dense air which moves in horizontally beneath it, hence becoming wind. However the whole process is complicated by the fact that the earth is rotating so that when the motion is on a large scale, circular patterns of air movement are formed resulting in rather stable high and low pressure areas which tend to drift westwards. Fairly standard patterns of warm and cold parcels of air and associated warm and cold fronts emerge.

On a smaller scale, land and sea breezes often occur around the New Zealand coast. In the daytime, the coastal land is heated by the sun and the air above it rises. The air over the cool sea remains fairly cold and dense so flows in to the replace the rising warm air. The wind coming in from the sea is called the sea breeze. Sometimes at night the air over the land becomes cooler than that over the sea and so becomes a land breeze flowing out to sea.