Pressure Gradient Force
The driving force for wind is the pressure gradient force. A pressure gradient is a difference in pressure over a given distance. The pressure gradient is usually indicated by the proximity of isobars (lines of constant pressure) on a surface weather map. Where several lines are tightly packed on a map, a large pressure gradient is said to exist.
An imbalance in pressure causes wind to blow as the atmosphere attempts to even out the pressure difference. The resulting force is always directed from the region of higher pressure to the region of lower pressure. Pressure differences usually occur as a result of heating differences on the earth’s surface. Large scale heating differences between the equator and poles produce the general circulation pattern of the atmosphere.
