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Thunderstorms
| Article
# : |
10255 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
8 / 1986 |
770 Words |
| Author
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Barbara Tufty
Barbara Tufty is a free-lance natural science writer
who lives in Washington, D.C. |
In late afternoon on a hot summer day, a wind breaks the oppressive heat, bends the grasses and shivers the leaves. A shadow skims across the ground, and the sky swiftly becomes overcast. From the dark underside of a cloud a sudden flash of lightning shoots forth, then a clap of thunder, and a downpour of rain. Another thunderstorm is lashing the earth.
At any moment, some 2,000 to 3,000 thunderstorms may be occurring in the world. They release enormous amounts of energy in the form of rain, hail, wind, thunder, lightning, and often tornadoes. Forming constantly in the tropics, thunderstorms occur most frequently in the warm spring and summer months in the temperate zones.
The frequency of these storms, and their violence and variety, make them one of nature's most consistently destructive forces. In the United States, lightning alone kills and injures some 600 people each year. Pelting hailstorms cause millions of dollars of damage by destroying crops and smashing windows, roofs of buildings, and vehicles. Flash floods from cloudbursts wash away houses and sections of highways, and sudden gusty downdrafts and squalls have capsized boats, flattened trees, and knocked over buildings.
Yet, these destructive storms are also beneficial. They help keep a balance of electrical discharge between the earth and the sky and bring essential rains to parched fields and forests. Even lightning, the great destroyer, sustains life by freeing nitrogen from the air which is washed by rain into the soil, and there becomes a vital element in the food chain for plants, animals, and humans.
A thunderstorm is a towering cloud system with storm "cells" of violent upward and downward air currents, powered by some of the most basic and wondrous dynamics of our planet. Thunderstorms are formed under unstable atmospheric conditions when warm moist air is lifted into cooler air by two kinds of convection: thermal, when the sun has been beating down on relatively flat locations, such as fields or forests, and warming the air over the ground; and mechanical, when a cold weather front moves in and pushes the warm air up.
As warm, moist air rises into higher, colder altitudes, the moisture begins to condense into tiny water droplets, and a cloud begins to become visible. This process of condensation releases latent heat energy into the cloud system, which further stokes the vigorous ascent of the updraft. As the updraft reaches higher into the atmosphere,
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