The Coriolis Effect

Air will always tend to flow from areas of higher pressure toward areas of lower pressure. This would make meteorology very easy if that were the only factor. However, the rotation of Earth complicates wind flow dramatically. Wind will appear to "turn" to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is called the Coriolis Effect.

It works like this. Consider an airplane that is traveling from Louisiana to Minnesota. Minnesota is approximately due north of Louisiana and this should be a straight trip, right? Well it is not that simple. In a car we could travel due north and reach our destination without a problem. In the airplane however, we must consider the rotation of the earth.

You are probably already aware that the sun rises in the east and sets in the west. That means if we were looking down from space we would see that the earth's equator turns toward the east.