However, air cannot always flow directly from high to low pressure because the Earth rotates and there is friction. The Coriolis Effect Friction Pressure-Gradient Force Wind is generated by horizontal pressure differences. When pressure hits the air more on one side than on the other a force is directed from the region of higher pressure to the region of lower pressure. These pressure differences cause the wind to blow, and the greater the differences, the greater the wind speed. In order to observe the differences in air pressure, meteorologists use isobars on surface weather maps.
Isobars are lines connecting places of equal air pressure.
The spaces between the isobars represent the amount of pressure change over a given distance. This is known as the pressure gradient . The relationship between wind speed and pressure gradient is directly related. A steep pressure gradient causes greater acceleration of air parcels than a weak pressure gradient does. The closer the isobars are to each other, the steeper the pressure gradient is, and the stronger the winds are.