Rotating Earth

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Rotating Earth

In thermal circulation, the assumption was made that the earth did not rotate, but of course this is not true. The rotation of Earth causes a force that affects thermal circulation, causing it to be deflected to the RIGHT of the direction of movement in the Northern Hemisphere and to the LEFT of the direction of movement in the Southern Hemisphere. This force is called the Coriolis force.

The Coriolis force is not a true force. It is an apparent force resulting from the west-to-east rotation of Earth. The effects, however, are real.

Arctic rivers cut faster into their right banks than their left ones. On railroads carrying only one-way traffic, the right hand rails wear out faster than the left-hand rails. Artillery projectiles must be aimed to the left of target because they deflect to the right. Pendulum clocks run faster in high latitudes than in lower latitudes. All these phenomena are the result of the Coriolis force, which is only an apparent force. The most important phenomena is that this force also deflects winds to the right in the Northern Hemisphere. Therefore, it is important to understand how this force is produced. As Earth rotates, points on the surface are moving eastward (from west to east) pasta fixed point in space at a given speed. Points on the equator are moving at approximately 1,000 miles per hour, points on the poles are not moving at all, but are merely pivoting, the points somewhere between are moving at speeds between 1,000 and zero miles per hour depending upon their relative position. Refer to view A in figure 3-1-4.

Assume that a missile located at the North Pole is launched at a target on the equator. The missile does not have any eastward lateral velocity, but the target has an eastward velocity of 1,000 miles per hour. The result is that the missile appears to be deflected to the right as the target

Figure 3-1-4.—Coriolis force.

moves away from its initial position. Refer to view B in figure 3-1-4.

A similar condition assumes that a missile located on the equator is launched at a target at the North Pole. The missile has an east-ward lateral velocity of 1,000 miles per hour; while the target on the pole has no lateral velocity at all. Once again the missile appears to be deflected to the right as a result of its initial eastward lateral velocity. Refer to view C in figure 3-1-4.

Due to Earth’s rotation and the Coriolis ef-fect, the simple circulation now becomes more complex as shown in figure 3-1-5. The complex circulation resulting from the interplay of the Cor-iolis effect with the flow of air is known as the 3-cell theory. (See fig. 3-1-6.)

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