What effect causes winds to curve due to Earth's rotation?

The Coriolis effect causes winds to curve because Earth rotates beneath moving air. In the Northern Hemisphere, moving air is deflected to the right of its path; in the Southern Hemisphere, it is deflected to the left.

The effect is apparent rather than a separate physical push: it appears when motion is described from Earth’s rotating reference frame. Its strength depends on latitude and speed. It is strongest near the poles and effectively zero at the equator, where the horizontal component vanishes.

Coriolis deflection helps shape large-scale weather systems, ocean currents, trade winds, jet streams, and the rotation of cyclones. It does not determine the direction water drains from an ordinary sink or bathtub; container shape and initial motion overwhelm the tiny effect at that scale.

The effect is named after French mathematician Gaspard-Gustave de Coriolis, whose 1835 paper analyzed forces in rotating systems. “Centrifugal force” is a common mix-up: it acts outward in a rotating frame, while Coriolis deflects moving objects sideways.