Page 40 - Beginner's Guide to Aviation
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The next 2 layers are the only atmospheric layers where commercial airliners cruise.
4. Stratosphere
Upper boundary: 50 km
Lower boundary: 8 km (at poles) / 10 km (at equator)
Aircrafts usually cruise pretty low in the Stratosphere at about 10 km to stay above heard weather and avoid turbulence. The Stratosphere also contains the ozone layer which protects us by absorbing most of the Sun’s ultraviolet radiation.
5. Troposphere
Upper boundary: 7km (at poles) / 17 km (at equator)
Lower boundary: Surface of Earth
The Troposphere is the lowest atmospheric layer which begins from the Earth’s surface. This layer is where most weather conditions such as thunderstorms occur.
These 2 layers have different values for its lower and upper boundaries due to the different in temperatures at the Earth’s poles and equator. The poles receive lesser solar energy as compared to the equator based on the differences in exposed surface area to due the Earth’s curvature. Therefore, the temperatures at the Earth’s poles are much cooler than the temperature at the equator.
As air expands in higher temperatures and contracts in lower temperature, the boundaries at the poles are lower than the boundaries at the equator.
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