Meteorology Charles A. Giannetta
Meteorologist - Professor
"The Hydrologic Cycle, a continuous process through the
interaction of the sun, earth, sea and atmosphere."
The atmosphere contains about 80% Nitrogen, 20% Oxygen and less
than 1% of all the other rare gases.
Most moisture in the atmosphere comes from the oceans. At one time
it was thought, most came from transpiration, the process by which
water in plants and trees is transferred as water vapor to the atmosphere.
Radiation from the sun heats the earth. As the water in the oceans
are heated, evaporation takes place, the process whereby water is
transformed in a gas, vapor, (LATENT HEAT OF EVAPORATION). The water
vapor mixes with the Nitrogen, Oxygen and all the other rare gases. As
the water vapor mixes in the atmosphere all the gases are displaced
proportionately. The atmosphere can hold only about 4% moisture.
Water evaporated from the ocean is distilled as it escapes as vapor
in the atmosphere.
As the water vapor rises in the atmosphere, it cools. If it rises
high enough, condensation occurs, the process whereby water vapor
changes to a liquid, (LATENT HEAT OF CONDENSATION). If the process
continues, the moisture in the clouds becomes heavy and falls back to
earth in the form of rain, snow, sleet, etc. Any of these forms are
called precipitation.
Most of the water which falls back to earth returns to the sea,
directly or through a network of rivers and streams. Some of the moisture
is absorbed by the root system of plants and trees. Water also penetrates
the ground down to the water table, the subterranean reservoir which
feeds springs and keeps streams flowing.
Annual rainfall in the United Sates is about 4 inches in the
desert regions to more than 100 inches in the mountain ranges of
Washington and Oregon. Here in Eastern Pennsylvania, the average
rainfall is about 45 inches.
"Weather By Giannetta"
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