A bright, sparkling, autumn day of crisp air, blue skies, clear sunshine? He feels invigorated, stands straighter, strides more optimistically into his day. A sweltering summer morning? He feels irritable, depressed, exhausted before the day’s work has hardly begun. Before he reaches the breakfast table, the weather colors and conditions man’s physical well-being, the state of his emotions, his attitude towards life.
Weather in its more benign form is the reason why one-tenth of the American nation lives in California, why the south-west desert country is booming, why the multi-billion-dollar space industry is springing up along the balmy Gulf Coast crescent.
This is a projection that would have been impossible 20 years ago, but it is now considered merely a routine preliminary to scientific forecasting.
All weather begins with 4 primary interacting elements. One is the sun, source of light and life, whose radiant energy ultimately determines the state of the atmosphere. Secondly comes the earth itself, whose unique geometry dictates the distinctive characteristics of weather and climate. The next element is the earth’s atmosphere, the envelope of gases that modulates solar radiation in its passage to earth. The fourth factor is made up of the natural land-forms and geophysical features of the earth’s surface — the mountains, valleys, oceans, ice-caps, deserts, lakes and rivers that alter the state of much of the atmosphere as it swirls incessantly around the earth.
Of the vast amount of energy that the sun radiates into space, the earth intercepts only a tiny fraction — about one two-thousand-millionth.
Without it, the earth would be a death planet, as sterile and lifeless as the moon; there would be no trees, no animals or birds, no bright sky, no clouds or golden sunsets. Not only is it essential because all life breathes it; it is also a necessary protective blanket. Without it, the rays of the sun would scorch the earth’s crust with temperatures as high as 80C by day. By night, the cold could reach an unendurable -140C.
If all of it were condensed in liquid form, it would cover the entire surface of the earth with 1 inch of rainfall.
The essence of weather is change. In minutes, the sea can turn from brilliant calm to towering storm. A shift in the wind can change an Indian summer’s day to a real foretaste of winter.
Changes in weather usually occur quickly. The life of a storm is measured in days, and even the great seasonal weather variations take place in the course of one journey of the earth around the sun. And so it is difficult to imagine the perennial snows of the last ice-age, when for 470,000 unbroken years a mantle of glaciers cover one-quarter of the earth.
A single small, fluffy cloud may hold from 100 to 1,000 tons of moisture.
The energy involved in these atmospheric chores is prodigious. A summer thunderstorm squanders in its profligate lifetime as much energy as a dozen or so Hiroshima-type bombs — and 45K thunderstorms are brewed around the earth everyday. A hurricane releases almost as much energy in one second.
The results were all very puzzling. Heat moved invisibly through space, it travelled in straight lines and it could be reflected. The theory was widely held that heat was an invisible substance, called “caloric,” that flowed from a warm body into a cooler until equilibrium was reached.
If all the earth’s atmosphere were clear and dry, the heat radiated from all the earth’s surfaces, including that from the tropics, would pass very quickly back into space. But three-quarters of the earth’s surface consists of water, and the skies overhead are loaded with water vapor to varying degree. Heat emanating from land and ocean is absorbed in abundance by vapor and cloud droplets, and re-radiated back to earth.
This giant tennis game played with infra-red rays is called the “greenhouse” effect.
The last stage in a hurricane’s life begins when it moves over land or colder water. Without warm, damp air the storm loses its energy. The cooler air cannot climb so high.
If the earth were stationary, the trade winds would blow directly from north to south in the Northern Hemisphere, and the opposite way in the Souther Hemisphere. But the spin of the earth, west to east, deflects or steers the traders — and in fact all winds of the general circulation — making them veer off their strictly north-south course.
Winds are the atmosphere in motion. They start to blow when warm air, expanding, is forced up, and cooled air, contracting, sinks. From this simple beginning the behavior of the winds grows almost inconceivably complex.