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Atmosphere, facts about the atmosphere

The entire surface of the Earth is covered by an immense 'sea' of air, stretching upwards to a height of several hundred miles. This covering of air is known as the atmosphere. It is usually thought of as consisting of three layers: the troposphere, which stretches from sea level to between 5 and 10 miles up; the stratosphere, which extends from between 5 and 10 miles up to 50 miles up; and the ionosphere, which lies beyond.

Atmosphere, facts about the atmosphere
The upper levels of the atmosphere are vital to long-distance radio communications because they reflect radio waves back to the ground, allowing them to travel around the Earth's curved surface. The Heaviside Layer reflects longer wavelengths, the Appleton Layer reflects shorter wavelengths. Very short wavelengths pass straight on into space, but they are sometimes reflected by meteor streams	By letting through most of the Sun's radiation, but trapping much of the Earth's longer wavelength radiation, the Atmosphere acts as a greenhouse over the Earth, keeping the temperature higher beneath it than above it

The air becomes 'thinned-out' as we move away from the Earth's surface. The oxygen that air contains is essential to all living creatures, so that man cannot survive at any great height without some kind of mechanical aid.

Even at heights of three miles or less, the thinning-out of the air is very noticeable, causing an uncomfortable shortness of breath. For this reason, mountaineers, especially when climbing the highest peaks, such as Mount Everest, are often forced to use oxygen masks to breathe.

Atmosphere, facts about the atmosphere
A jet stream is a channel of quickly-moving air occurring at about 30,000 feet. At its center, air is traveling at between 100 and 200 miles per hour	Temperatures in the atmosphere

Life as we know it is possible because our Earth has an atmosphere. To appreciate the importance of the atmosphere, consider the Moon, which has no atmosphere. Temperatures in the daytime are so high that if the Moon had any water it would boil. And at night it is very much colder even than the coldest places on Earth. But on Earth the atmosphere acts as a shield during the day, protecting us from the Sun's rays, and as a blanket at night, holding the heat in. We do not usually think of air as having weight, but in fact it has. The total weight of the atmosphere is nearly 6,000 million million tons. The column of air rising above each of us weighs about a ton and exerts a pressure of about 15 pounds on every square inch at sea level. We do not notice this tremendous pressure because the pressure inside our bodies is the same as that outside, just as the pressure inside deep-sea creatures is the same as the tremendous pressure of the surrounding water.

Atmosphere, facts about the atmosphere: the composition of air

The higher we go in the atmosphere, the lower the pressure, because there is less air above us and, as a result, less weight of air. Thirty miles up, the air pressure is only one-thousandth of the air pressure at sea level.

Conditions in the troposphere, the lowest layer of the atmosphere, create the world's weather. In the troposphere, temperatures usually decrease with height at the rate of 3-5° F for every thousand feet (6° Ñ for every thousand meters). But at the boundary between the troposphere and the stratosphere above, the temperature stops falling for a while. This is called the tropopause. In certain places along the tropopause there are winds of over 100 miles per hour. These are called jet streams.

One more interesting fact: the stratosphere is generally much calmer than the troposphere and is used by high-flying aircraft to avoid bad weather conditions. The outermost layer of the atmosphere, the ionosphere, is important in long-range radio communications. It reflects medium and long radio waves back to the ground, making it possible for them to travel around the Earth's curved surface.

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