Kelly Gatto, age 12, of Loudonville, N.Y., for her question:
DO THE CLOUDS MAKE THE WIND BLOW?
Sometimes it looks that way. On certain breezy days, teams of dashing clouds seem to be driving the wind across the sky. But things up there tend to fool the eye. In this case, the wind always drives the clouds.
It is not easy to understand why or how the wind blows. This is because it is invisible and so are the forces that cause it to move. Certainly the clouds do not cause it. They just happen to be in the way and get themselves blown along in the draft.
Actually, even the wildest wind is no more than a draft of moving air. And the air is invisible because it is made of widely separated mini molecules, too small for our eyes to see. These gaseous molecules are full of peppy energy, dashing around in all directions even when the air seems to be calm and still. They move because in some mysterious way they can change heat into driving energy.
Temperatures work behind the scenes to set the breezy winds in motion. And, as we know, the global temperature changes because the sun warms the earth in uneven patches. The air gets its warmth from the surface of the land and sea so the air heats up in uneven patches. This means that some air masses have more peppy energy than others.
As a mass of air becomes warmer, its molecules use the extra heat energy to speed up and spread farther apart. This makes the air mass thinner and lighter. It creates what the weatherman calls a region of low pressure. This airy pocket weighs less than the air around it.
Meantime the global atmosphere strives to keep itself evenly balanced. This causes the different air masses to mix and mingle. And how do you think they do it? Naturally, the masses of heavier high pressure air blow into the thin low¬pressure masses. The drafty winds blow somewhat as water flows downhill, from high to low.
The strength of the wind depends on how fast the drafty air is moving. Even a gentle breeze is strong enough to move the soft fluffy clouds lazily across the sky. The raging gales of a howling hurricane drive a skyful of heavy rain clouds. And when the wind dies down, all the clouds come to a stop.