Shawn Jessup, age 12, of Spokane, Wash., for his question:

HOW COME MOUNTAINTOPS COLDER THAN LOWLANDS?

In summer, the high mountain slopes are cooler than the plains and valleys below. In winter, the first snows tend to settle on the tall peaks, where they linger long after the snow has melted from the lowlands.

The planet earth, as we know, is warmed by the fiery furnaces of the sun. True, we are separated from this stupendous nuclear power plant by about 96 million miles of unoccupied space. But surely one would expect the mountaintops to be warmer than the lowlands. For their lofty peaks are from 1 to 5 miles closer to the solar furnace.

    However, solar energy works in mysterious ways to shed more warmth on the plains and less on the lofty peaks. For example, in the torrid tropics, many high mountains wear snowy crowns throughout the year. Obviously we cannot expect to gain more warmth by moving a few miles closer to the sun. This is because of the earth’s atmosphere and the nature of solar energy.

We can figure our quota of solar radiation as a sort of energy budget. On its way down to the surface, about 40$ of the quota is reflected back into space by clouds, which normally hover above half the surface. On the way down, very little is absorbed by the airy atmosphere. The warmth is shed onto the solid land and liquid oceans, where certain solar wavelengths are converted into heat.

Some of this solar heat is used to warm land and oceans, some to evaporate moisture. Some is absorbed by the lower level of the atmosphere. Since the air gets most of its heat from the surface, we would expect it to be warmer at lower levels and cooler at the upper levels. As a general rule, this proves to be true. The air grows cooler as we rise higher above the surface of the planet. Mountain peaks tend to be cooler than the lowlands because the air absorbs its heat from the surface.

However, the global atmosphere is in a constant state of weathery turmoil. The surface of the planet gets its heat in uneven patches. Above it, masses of warm and cool air blow hither and yon. and sometimes a mass of warm air slides up and over a mass of cool air. Then, once in a while, a pocket of upper air is warmer than the air below it.