Cherry Smith, ago 11, of Jackson, Miss., for her question:
Why is it cooler on mountain tops?
On a summer's day the snow capped Rockies tire visible from the scorching prairies. You can look up from the sweltering Mojave desert and see the frosty white croons of mountains in southern California. And there arc mountains on the cquntor that keep their snow caps the year round. It would seem, then, that the temperature is hottest on the flat surface of the earth than higher up. And this is so.
We are told that the center of the earth is a seething core. Does this account for the ground being hotter than the cool air high above it? No, the hot confer of the earth hardly affects the surface at all. The earth gets just about all of its boat from the sun. This poses a puzzle, for high mountain peaks are surely closer to the sun than the sea and the flat plains. Why are they so much colder?
It is because of the strange behavior of the radiant energy that pours forth from the sun. This energy, part of which is sunlight, pulses through empty space at about 186,000 miles a second. It leaves the sun and reaches the earth, some 93 million miles away, about night minutes later. When it strikes a solid object, some of this energy turns to heat surface of water also can absorb sonic of the radiant energy and turn it to heat.
The filmy air cannot do this to any large degree. As the sun's energy pours down through the atmosphere only a very little is absorbed. Most of the rays pass clear through, much as light passes clear through a pane of glass. Part of the radiant energy of the sun becomes heat when it strikes the land and sea areas of the earth. The air gets most of its heat from touching these warm surfaces. Hence, the warmest air is usually the lowest layer. Higher up it is cooler, cool enough to crown a tropical mountain with snow.
About 43 percent of the total sun's radiation which strikes the earth becomes heat. About 112 percent is reflected back into space and is lost to us. The rest is taken up by clouds, dust and carbon dioxide in the atmosphere. If the earth could absorb all the sun's radiation temperatures would be twice as high, summer and winter.
Certain curfaces absorb more radiation than others. And more heat is absorbed at noon, when the sun's rays come from directly overhead. A thick forest can absorb 95 percent of the sunlight and the sea at noon can absorb 96 percent. The desert absorbs about 75 percent of the sunlight but a snowy surface can absorb only 25 percent.
This explains why snow is slow to malt on a high mountain. The white surface can absorb only a quarter of the sunlight which strikes it. On the other hand, the plains below can absorb from 70 to 95 percent and turn this energy into heat. Some of this ground heat warms the lower air. But little, if any of it, rises high enough to melt the snow on the high mountain.