All around the earth, environmental scientists observe fairly steady patterns of wind (or directions of airflow). These prevailing winds, as they’re often called, are the result of the air being moved by convection currents (the Hadley cells at the equator and other convection cells near the poles and mid-latitudes) combined with the Earth’s rotation.

As air moves away from the mid-latitudes toward the poles and toward the equator, it doesn’t move in a straight line relative to the earth’s surface. Rather, it moves in a slightly curved direction as a result of the Earth’s rotation. This phenomenon is called the Coriolis effect.

To help you visualize how the Coriolis effect works, imagine that you’re standing at the North Pole and tossing a baseball toward the equator. While the ball travels through the air, the Earth below it is rotating, so when the ball reaches the equator, it lands in a location somewhere to the west of where you were aiming. The figure illustrates this example.

[Credit: Illustration by Wiley, Composition Services Graphics]
Credit: Illustration by Wiley, Composition Services Graphics

Near earth’s surface, the Coriolis effect creates wind (and water) patterns that move to the east toward the equator and to the west toward the poles. These prevailing wind patterns are responsible for moving clouds around the globe and, thus, for creating patterns of weather in different regions.