JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
JX101 - ATMOSPHERIC STRUCTURE
OVERVIEW
This lesson will discuss the basic building blocks of the atmosphere, beginning with the lower
layers in which most flight activity occurs. These layers have particular temperature
characteristics that affect many aspects of weather, and thus are important to the understanding
of later chapters. Pressure is another characteristic of the atmosphere which enables
meteorologists to track weather phenomena as they move across the surface of the earth.
Additionally, pressure is important to the aviation community since one of the most basic flight
instruments, the barometric altimeter, operates from the action of atmospheric pressure upon its
sensors. In order to gain a complete understanding of the altimeter, the effects of temperature and
pressure variations on altimeter readings will also be discussed.
REFERENCES
AFH 11-203, Weather for Aircrews, Volume 1, Chapters 1, 3, and 4.
THE ATMOSPHERE
The atmosphere is the gaseous covering of the Earth. This envelope of air rotates with the Earth
but also has a continuous motion relative to the Earth’s surface, called circulation. It is created
primarily by the large temperature difference between the tropics and the polar regions, and is
complicated by uneven heating of land and water areas by the Sun.
Atmospheric Layers
If the Earth were compared to a baseball, the gaseous covering would be about as thick as the
baseball’s cover (Figure 1-1).
Figure 1-1 — Thickness of the Earth’s Atmosphere
It is divided into layers that have certain properties and characteristics (Figure 1-2). The
troposphere is the layer adjacent to the Earth’s surface. It varies in height from an average 55,000
feet over the equator to 28,000 feet over the poles.
1-1 Version 3.2/Dec 08