Bill Vos, age 13, of St. Paul, Minn., for his question:

WHAT CAUSES THE WEATHER TEMPERATURE TO CHANGE?

The changeable weather seems to do as it pleases, though actually there are global patterns behind the scenes. Summers are warmer and winters are cooler; a scorching hot day tends to cool off after sundown. The tropics are warmer than the temperate and polar zones. Obviously these weathery temperatures must be governed by global forces behind the scenes.

All the warmth in the atmosphere comes from the sun, though in a rather roundabout way. Patches of solar heat cause temperatures to rise. When the warmth departs the temperatures fall, for coldness is merely absence of heat. The fiery furnace of the sun pours forth its radiant energy at a fairly steady rate. Hence one would expect the entire earth to be comfortably warm at all times and in all places

This does not happen because the earth itself causes an unequal distribution of the sun’s generous energy. If our planet were a flat table top, tilted to face the sun, maybe the entire surface would get the same steady quota of solar radiation. However, it is a round globe. What’s more, the dizzy old globe constantly spins on its tilted axis and endlessly orbits the sun.

The shape and the motions of the earth cause the surface to heat up in uneven patches. The air absorbs most of its warmth from warm areas of lands and oceans. Gaseous air molecules use this energy to speed up and spread apart. They rise, lose some of their heat, slow down and the temperature falls.

Surface temperatures change with the seasons, with day and night and between the poles and the equator. Oceans tend to be warmer than the land in winter and cooler in summer. The air gets its warmth from these uneven areas—and the atmosphere is more restless than the fluid oceans.

Masses of cool, heavy air tend to flow and blow toward masses of light, warm air. The breezy weather is kept in a constant state of turmoil, as warm and cool air masses mix and mingles,  changing the temperature from moment to moment.

Everywhere the air gets its warmth from uneven patches of warmth on the surface. Local breezes blow between lands and seas, changing temperature as they go. On a grand scale, great planetary winds sweep around the globe, mixing and mingling temperatures between the warm equator and the icy poles. And the patchwork changes as the dizzy old earth rotates and revolves.