by Jonathan M. Stern
Low and high pressure areas form and affect the weather in rather significant ways. Figure 13.2 shows an example of pressure systems in the continental United States.
Figure 13.2. An example of pressure systems in the continental United States.
If the Earth did not rotate, wind would blow directly from highs to lows. The force that creates such winds is referred to as pressure gradient force, and it is greater when the pressure changes over smaller distances and lesser when the pressure changes occur over a greater distance. Meteorologists plot lines of equal pressure, which are called isobars, to visualize the pressure gradient and the locations of highs and lows.
The rotation of the Earth introduces Coriolis force, which, in the Northern Hemisphere, causes the wind to deflect to the right and to parallel the isobars. As a result, in the Northern Hemisphere, airflow around a high pressure area is clockwise and counterclockwise around a low pressure area.