An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The apparent → deflection of a body in motion with respect to the Earth, as seen by an → observer on the Earth, caused by the → Earth's rotation. Thus, a projectile fired due north from any point on the northern hemisphere will land slightly east of its target (deflection to the right). This involves two factors: 1) the eastward velocity of Earth's surface decreases from the → equator to the → poles, and 2) when an object starts to move north or south without being firmly connected to the ground it maintains its initial eastward speed (conservation of → angular momentum). Hence, an object travelling away from the equator will be heading east faster than the ground and will seem to be forced east. On the other hand, a ball fired in the northern hemisphere toward the equator deflects to the west. As for the southern hemisphere, a ball fired southward will deflect East. The projectile is not subject to this effect only on the equator, when it is thrown in an east-west direction. The Coriolis effect is therefore greater at higher → latitudes and smaller near the equator. This effect is of paramount importance to the large-scale → atmospheric circulation, the development of storms, and the sea-breeze circulation. In low pressure systems, i.e. zones where air ascends, the air is less dense than its surroundings and this creates a center of low atmospheric pressure. Winds blow from areas of high pressure to areas of low pressure, and so the surface winds would tend to blow toward a low pressure center. But, because of the Coriolis effect, they are deflected. In the northern hemisphere they are deflected toward the right, and fail to arrive at the low pressure center, but instead circulate around it → counterclockwise. In the southern hemisphere the circulation around a low pressure center would be → clockwise. Regarding high pressure systems in the northern hemisphere, a general clockwise rotation is created around the center. Same as the → Coriolis force. See also → geostrophic wind, → geostrophic flow.

Named after Gaspard Gustave Coriolis (1792-1843), French engineer and mathematician who first described this effect; → effect.