What is the Coriolis effect ?

  The Coriolis effect is the apparent curvature of global winds, ocean currents, and

everything else that moves freely across the Earth’s surface. The curvature is due to the

rotation of the Earth on its axis. In physics, the coriolis effect is an apparent deflection of

moving objects when they are viewed from a rotating reference frame. In a reference frame

with clockwise rotation, the deflection is to the left of the motion of the object, in one with

anti-clockwise rotation, the deflection is to the right.The effect was discovered by the

nineteenth century French engineer Gaspard C. Coriolis. He used mathematical formulas to

explain that the path of any object set in motion above a rotating surface will curve in relation

to objects on that surface.

What causes the Coriolis effect ?

The Coriolis effect is caused by a combination of the inertia of moving air and the rotation of

the Earth. Air tends to move from high pressure to low pressure in a straight line, but the

rotation of the Earth means that, to an observer at one spot on its surface, the moving air

appears to turn. This effect increases as the air moves faster. The Coriolis effect is an observer

effect. For example, a passenger on a moving train watching another person standing still

outside the train. The person outside the train appears to be moving. In the same way, air

currents appear to be moving off to one side of their original path under the Coriolis effect,

but it is actually the observer that moves. In this case, the rotating Earth is like the moving

train, carrying the observer along. Air is not affected as strongly, so it appears to change

direction. The directional change is always toward the west.The Coriolis effect is most

evident in air moving directly north or south. It not only affects the air but also any projectile

traveling through the air. For instance, a ballistic shell fired directly southward from the North

Pole will land somewhat west of a target placed due south.

Why is the Coriolis effect important ?

If not for the Coriolis effect and Earth’s rotation, global winds would blow in straight north-

south lines. What actually happens is that global winds blow diagonally. The Coriolis effect

influences wind direction around the world in this way, in the Northern Hemisphere it curves

winds to the right, in the Southern Hemisphere it curves them left. The exception is with low

pressure systems. In these systems there is a balance between the Coriolis effect and the

pressure gradient force and the winds flow in reverse. Without the coriolis effect, winds

would tend to blow from north to south, making the cold climate extend further south. The

coriolis effect also causes ocean currents to be more intense in the western ocean basins.

Satellites appear to follow curved paths when plotted on world maps because the Earth is a

sphere and the shortest distance between two points on a sphere is not a straight line. In the

northern hemisphere a satellite’s orbit using the shortest possible route will appear to follow a

path north of the straight line from beginning to end, and then curve back toward the equator.

This occurs because the latitudes, which are projected as straight horizontal lines on most

world maps, are in fact circles on the surface of a sphere, which get smaller as they get closer

to the pole. This happens simply because the Earth is a sphere and would be true if the Earth

didn’t rotate. The Coriolis effect is of course also present, but its effect on the plotted path is

much smaller, but increases in importance when calculating a trajectory or end destination.

To sum up ‘why is the Coriolis effect important ’, it is an important meteorological force that

is used to predict the path of storms and explains why a projectile will not hit a target at a

great distance if the Earth’s rotation is not accounted for.

Where is the Coriolis effect the weakest ?

It is weakest near the equator and strongest at the poles. It is because a result of rotation of a

curved surface. The radius of curvature decreases as you go poleward, thus the effect is

magnified. Since the surface rotates less as you go poleward, the momentum of anything in

motion but not in contact with the surface causes the effect of an apparent turn to the right as

it moves, due to the change in speed of the Earths surface below.

Why Geostrophic wind is not possible at the equator ?

The geostrophic wind is the theoretical wind that would result from an exact balance between

the Coriolis effect and the pressure gradient force. This condition is called geostrophic

balance. Geostrophic wind is not possible at the equator because the Coriolis effect is weak at

the equator and the Geostrophic wind requires a balance between the pressure gradient force

and the Coriolis force. However, the Coriolis force is zero at the equator because there

is no pressure gradient force at the equator.

REFERENCES

Holton, J.R., 'An Introduction to Dynamic Meteorology', International Geophysical Series, Vol 48 Academic Press.

ww2010.atmos.uiuc.edu abyss.uoregon.edu http://www.princeton.edu/~achaney/tmve/wiki100k/docs/

Coriolis_effect.html