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Wan LixinOpinion deputy editor of Shanghai Daily
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Why does the temperature get hotter as we go lower?
April 5, 2010, Monday
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THE air in the atmosphere gets denser as the elevation gets lower. As solar radiation (called short-wave radiation) makes its way through the atmosphere, some of it gets scattered and reflected, with the remainder being absorbed by the ground.
At a lower elevation, the denser air tends to scatter and reflect more of this incoming solar radiation than the thinner air found at higher elevations. But the Earth's atmosphere is rather transparent to this short-wave radiation, so the atmosphere doesn't get heated up much by this direct radiation from the sun.
Even at lower elevations, the effect of this increase in this scattering and reflection pales in comparison to another process at work - the absorption of long-wave radiation by the atmosphere from the earth's surface.
So what exactly is this long-wave radiation? The Earth's surface absorbs the short-wave radiation from the sun, and returns this energy as long-wave radiation (or just simply heat energy) to the atmosphere. Now this long-wave radiation is easily absorbed by the air and water vapor, and this is the main process that heats up the lower atmosphere. Thus the atmosphere is heated from the bottom up. The effect of this heat absorption is more pronounced at a lower elevation, where the atmosphere is denser.
The energy absorbed by the atmosphere helps to heat the ground surface in turn, creating the heating mechanism known as the greenhouse effect. So, a denser layer of air traps more long-wave radiation due to a more pronounced greenhouse effect - and that's why it gets hotter the lower we go.
At a lower elevation, the denser air tends to scatter and reflect more of this incoming solar radiation than the thinner air found at higher elevations. But the Earth's atmosphere is rather transparent to this short-wave radiation, so the atmosphere doesn't get heated up much by this direct radiation from the sun.
Even at lower elevations, the effect of this increase in this scattering and reflection pales in comparison to another process at work - the absorption of long-wave radiation by the atmosphere from the earth's surface.
So what exactly is this long-wave radiation? The Earth's surface absorbs the short-wave radiation from the sun, and returns this energy as long-wave radiation (or just simply heat energy) to the atmosphere. Now this long-wave radiation is easily absorbed by the air and water vapor, and this is the main process that heats up the lower atmosphere. Thus the atmosphere is heated from the bottom up. The effect of this heat absorption is more pronounced at a lower elevation, where the atmosphere is denser.
The energy absorbed by the atmosphere helps to heat the ground surface in turn, creating the heating mechanism known as the greenhouse effect. So, a denser layer of air traps more long-wave radiation due to a more pronounced greenhouse effect - and that's why it gets hotter the lower we go.
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