The Earth’s Oceans and Atmosphere
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When we think of the atmosphere, we think of winds. But winds are just a local reflection of the global circulation of the atmosphere. The amount of heat coming up from the Earth’s interior to its surface is very small compared with the amount of heat that the surface receives from the Sun. In consequence, it is solar heat that drives all the motions we see in the atmosphere and the oceans. Suppose that the Sun is overhead at the equator. The surface of the Earth must be heated more there than elsewhere. This means that the air above it is also heated more. As a result of the heating, the air becomes less dense and rises (like a hot-air balloon). It continues upward for a while until it reaches a stable layer of the atmosphere, called the stratosphere, at a height of about ten kilometers. This forms a barrier that prevents further motion upward. As a result, the air north of the equator is deflected sideways and starts moving northward. (Movements in the atmosphere south of the equator are mirror images of movements in the northern atmosphere. So heated air south of the equator correspondingly moves southward.) As this warm air moves to higher latitudes, it loses its heat and becomes denser again, making it fall back toward the Earth’s surface. It has one more journey to make. The next lot of air at the equator has by now been heated and risen upward. The old air must therefore flow back to the equator to fill the gap. This is the same kind of roundand- round flow that we have seen before, and called convection. The result is a continuing circulation that produces northerly winds in the upper atmosphere north of the equator, together with southerly winds at the surface. An atmospheric motion of this kind is called a cell.
KeywordsGreenhouse Effect Solar Eclipse Solar Heat Continental Drift Night Side
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