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Pilot's Handbook of Aeronautical Knowledge
Weather Theory


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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Layers of the atmosphere.
Figure 11-2. Layers of the atmosphere.


The atmosphere is a blanket of air made up of a mixture of
gases that surrounds the Earth and reaches almost 350 miles
from the surface of the Earth. This mixture is in constant
motion. If the atmosphere were visible, it might look like
an ocean with swirls and eddies, rising and falling air, and
waves that travel for great distances.

Life on Earth is supported by the atmosphere, solar energy,
and the planet's magnetic fields. The atmosphere absorbs
energy from the Sun, recycles water and other chemicals, and
works with the electrical and magnetic forces to provide a
moderate climate. The atmosphere also protects life on Earth
from high energy radiation and the frigid vacuum of space.

Composition of the Atmosphere
In any given volume of air, nitrogen accounts for 78 percent
of the gases that comprise the atmosphere, while oxygen
makes up 21 percent. Argon, carbon dioxide, and traces of
other gases make up the remaining one percent. This cubic
foot also contains some water vapor, varying from zero to
about five percent by volume. This small amount of water
vapor is responsible for major changes in the weather.
[Figure 11-1]

The envelope of gases surrounding the Earth changes
from the ground up. Four distinct layers or spheres of the
atmosphere have been identified using thermal characteristics
(temperature changes), chemical composition, movement,
and density. [Figure 11-2]

Composition of the atmosphere.
Figure 11-1. Composition of the atmosphere.

The first layer, known as the troposphere, extends from sea
level up to 20,000 feet (8 kilometers (km)) over the northern
and southern poles and up to 48,000 feet (14.5 km) over the
equatorial regions. The vast majority of weather, clouds,
storms, and temperature variances occur within this first layer
of the atmosphere. Inside the troposphere, the temperature
decreases at a rate of about 2 ┬░Celsius (C) every 1,000 feet
of altitude gain, and the pressure decreases at a rate of about
one inch per 1,000 feet of altitude gain.