Man's physical universe

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CLIMATE AND WEATHER 259

twenty-five layers and are very large in size. Hailstorms may be very

destructive, ruining crops, killing livestock, and breaking windows.

There are two kinds of thunderstorms; the local thunderstorm generally

follows an extremely hot day and moves in no certain path,

although the prevailing winds determine its direction somewhat; the

more severe thunderstorm is the result of a great current of cold air,

often hundreds of miles across, flowing against a current of moist hot

bodily by sliding in under it.

air and lifting it

Thunder squalls, or line squalls, are often very destructive because

of the great velocity of the wind. This wind results from the motion of

the huge air mass, in part, but is due chiefly to the outward and downward

rush of air produced by the descending current of cold air resulting

from the evaporation of the rain.

Thunderstorms occur very frequently in certain mountain regions;

for example, on Pikes Peak there is a thunderstorm nearly every

afternoon in the summer. Hot, moist regions like those surrounding

the Gulf of Mexico have frequent thunderstorms, whereas thunderstorms

on the Pacific coast are very rare.

Cloudbursts Are Sometimes Produced by the Conditions That Attend

Thunderstorms.

Sometimes rain is prevented from falling by rising air currents until

extraordinary amounts of water have accumulated. Suddenly the

supporting force weakens, and the

water descends as a so-called cloudburst.

At Cherrapuaje, India, 40.8

inches of rain fell in one day on

June 14, 1876. Here the average annual

rainfall is 426 inches, amounting

to about 50,000 tons per acre.

Tornadoes and Waterspouts Are

Violent Whirls in the Atmosphere.

Sometimes upward convection

leads to a whirling motion of the

ascending column, which may produce,

according to circumstances,

an ordinary whirlwind, a tornado, or

a. waterspout. A whirlwind may happen

to rotate in either direction and is produced in much the same way

as the whirl in water draining out of a basin.

Fig. 80. Tornado of May 4, 1922,

Austin, Texas. (Courtesy of the U. S.

Weather Bureau.)

On the other hand, the

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