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Tutorial
2(a). Atmosphere
Though we live on the surface of the Earth, we actually
live at the bottom of an ocean of air. Dynamic layers of air interact with the
Earth's surface and the Sun's energy to produce the phenomenon of weather. The
atmosphere is classified into layers based upon the characteristics each layer
exhibits. Most weather occurs in the troposphere and most flying occurs in the
troposphere and stratosphere. The atmosphere is comprised of air. Air is a mixture
of gases. It is about 80 percent nitrogen and 20 percent oxygen. Water vapor
and many other gases constitute the remainder of the gas mixture. Air is made
up of matter and has weight. Since air is gaseous, it is compressible. This
means that the air pressure nearer the surface of the Earth is greater than
the air pressure in the stratosphere. Air exerts pressure on everyone and everything.
At the Earth's surface the pressure is 14.7 pounds per square inch. That does
not sound like much, but it means the air pressure per square foot is 2116.8
pounds. Increase the air pressure and the air's density is increased. Because
of air's compressibility flight conditions will vary depending upon the altitude.
This is due to the air density. More molecules in the air will generate greater
lift with less thrust. Fewer molecules in the air will require greater thrust
to generate adequate lift. The decrease in air density with increase in altitude
also affects people physiologically. Decrease the air pressure and the oxygen
pressure is also decreased. The rate at which our lungs absorb oxygen depends
on the partial pressure exerted by the amount of oxygen in the air. Since our
atmosphere is about 1/5 oxygen, the oxygen pressure at any given altitude will
be about 1/5. Under normal conditions our lungs function under 3 pounds per
square inch of oxygen pressure. As an airplane climbs higher into the troposphere,
it will encounter less oxygen. Without supplemental oxygen the people on board
such a flight will suffer from hypoxia, a deficiency in oxygen. The symptoms
of hypoxia are a feeling of acute exhaustion with an immediate impairment in
vision and judgment resulting in unconsciousness and death if the proper amount
of oxygen is not soon administered. Prolonged flights at or above 10,000 feet
and even short flights above 12,000 should use auxiliary oxygen.
The ocean of air we live in can be calm, delightfully warm and pleasant or it
can be turbulent and rainy like a thunderstorm, hurricane or tornado. The air
temperature varies from below -100 Celsius to above 1500 Celsius (-150 Fahrenheit
to 2700 Fahrenheit). These variations are caused by the uneven heating of the
Earth's surface by the sun's energy as well as how the Earth reacts to this
energy. The characteristics of a substance (for example water or land) will
affect the amount of heat absorbed or released by that substance. Let's say
we have a land surface and water surface of equal temperature and we apply an
equal amount of heat to each. The land surface will become hotter at a much
faster rate than the water surface. The opposite is true when both substances
release the same amount of heat. Under equal heat loss the land will become
colder at a faster rate than the water.
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