- ATMOSPHERE:
The atmosphere consists of all the gasses that surround our planet.
The atmosphere is arranged in layers. From lowest to highest, these layers are:
- Troposphere (from 0 to about 12 km up):
This is the familiar part of the atmosphere, containing most of the gasses.
All airplane flights and nearly all weather phenomena take place within the Troposphere.
The air in the Troposphere is about 79% nitrogen (N2), 20% oxygen (O2),
0.9% argon (Ar), and 0.1% or less of everything else.
The outer limit (top) of the Troposphere, where it stops or pauses, is called the tropopause.
The height of the tropopause actually varies with latitude (higher above the Equator, lower above the poles) and seasonally (higher in summer, lower in winter).
- Stratosphere (from about 12 km to about 50 km up):
The lower part of the Stratosphere is rich in ozone (O3) and is called the ozone layer. This layer screens out
most dangerous (cancer-causing) ultraviolet rays from reaching Earth's surface.
The stratosphere does contain some ice-crystal clouds, but only in polar regions.
The outer limit (top) of the Stratosphere, where it stops or pauses, is called the stratopause.
- Mesosphere (from about 50 km to about 82 km up):
Meteors from outer space usually burn up within the Mesosphere.
The outer limit (top) of the Mesosphere, where it stops or pauses, is called the mesopause.
- Thermosphere (from about 82 km to about 600 km up):
The Thermosphere gets its name from the fact that temperature within this layer increases with height, to as hot
as 500 to 2,000 degrees Celsius, hotter by day than at night.
The Aurora Borealis ("Northern lights") and Aurora Australis ("Southern lights") occur within this layer.
Most artificial satellites circle the Earth within the Thermosphere.
The outer limit (top) of the Thermosphere, where it stops or pauses, is called the thermopause. Its height fluctuates quite a lot.
- Exosphere (above 600 km):
Sometimes considered to be "above" the atmosphere because there is little or no gas in it.
- The Ionosophere contains lots of electrically charged (ionized) particles, but it does not form a distinct layer.
Instead, the ionized particles that make up the ionosphere occur in patches or clouds at varying altitudes (in the Mesosphere, Thermosphere, or Exosphere).
Radio waves are reflected back to Earth by the Ionosphere.
|