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The earth's rotation
creates an apparent force ("Coriolis force") that deflects
moving air to the right of its initial direction in the Northern
Hemisphere and to the left of its initial direction in the Southern
Hemisphere.
The magnitude of the
deflection, or "Coriolis effect," varies significantly with
latitude. The Coriolis effect is zero at the equator and increases to a
maximum at the poles. The effect is proportional to wind speed; that is,
deflection increases as wind strengthens. The resultant balance between
the pressure force and the Coriolis force is such that, in the absence
of surface friction, air moves parallel to isobars (lines of equal
pressure). This is the geostrophic wind.
The Coriolis force
explains why winds circulate around high and low pressure systems as
opposed to blowing in the direction of the pressure gradient.
The following figure
shows how wind is deflected in each hemisphere:
The
effect of the Earth's rotation on the atmosphere and on all objects on the
Earth's surface. In the northern hemisphere it causes moving objects and
currents to be deflected to the right; in the southern hemisphere it causes
deflection to the left.
As air begins flowing from high to low pressure, the
Earth rotates under it, making the wind follow a curved path. In the Northern
Hemisphere, the wind turns to the right of its direction of motion. In the
Southern Hemisphere, it turns to the left. The Coriolis force is zero at the
equator.
Gaspard de Coriolis
The effect is named
after its discoverer, French mathematician Gaspard de Coriolis (1792–1843)
Credit: NOAA, NSIDC |
