Had the earth not been rotating about its axis the winds would  have blown in the direction of pressure gradient. The earth on account of its rotation produces a force known as Coriolis force after the name of the mathematician Coriolis. This force displaces the winds from the direction of the wind gradient. Ferrel formulated a law to reduce the direction of winds in the northern and southern hemispheres. It is known as Ferrel's law.

According to Ferrel's law, if we stand without faces in the direction in which the wind is blowing the wind will turn towards our right hand in the northern hemisphere and towards our left hand in the southern hemisphere.

The axial rotation of the earth has no effect on the direction of winds in the equatorial areas but as we move towards higher latitudes the effect of axial rotation is increasingly felt. This effect is maximum at poles.

Had there been no axial rotation the winds would have blown at right angles to the isobars but due to this rotation the winds blow almost parallel to the isobars. This condition is found at a height of 1000 m from the surface of the earth where the friction between the winds and earth's surface is reduced to zero. Below this height the friction comes effective and reduces the force due to the earth rotation. Hence the winds in the lower atmosphere strike the isobars at an acute angle of 20°-25°.

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