Environment

Why do weather systems travel west to east, moving more quickly than Earth’s rotation does?    

Arnold Behrer, via the Internet

Scott Kiser, a meteorologist at the National Weather Service in Silver Spring, Maryland, replies:

Newton’s laws of momentum dictate that as Earth rotates west to east, the atmosphere rotates along with it in a counterclockwise, or west-to-east direction. High temperatures and atmospheric pressures at the equator and low temperatures and pressures at the poles create the winds associated with weather. As air flows from high to low pressure, Earth’s rotation deflects air in both the Northern and Southern Hemispheres in a basic west-to-east direction. This deflection is known as the Coriolis effect. It creates a belt of strong west-to-east winds called the westerlies, which blow along the middle latitudes about five to seven miles above the ground. The combination of Earth’s rotation and the wind causes weather systems to move more quickly than the rotation itself. Excess speeds are caused by dramatic differences in pressure, which force air molecules to rush toward lower-pressure areas. Embedded within westerly air flows are narrow ribbons of high-speed winds, collectively known as the jet stream. At the middle latitudes, jet stream winds can blow up to 200 miles per hour faster than the rotation of the solid Earth below.