The Atmosphere is divided into layers according to major changes in temperature.
Gravity pushes the layers of air down on the earth's surface. This push is called air pressure. 99% of the
total mass of the atmosphere is below 32 kilometers.
Troposphere - 0 to 12 km - Contains 75%
of the gases in the atmosphere. This is where you live and
where weather occurs. As height increases, temperature decreases. The temperature drops about 6.5 degrees Celsius for every kilometer above the earth's surface.
- Tropopause - located at the top of the troposhere. The temperature remains fairly constant here.
This layer separates the troposphere from the stratosphere. We find the jet stream here. These are very strong winds that blow eastward.
Stratosphere - 12 to 50 km - in the lower part of the stratosphere. The temperature remains fairly
constant (-60 degrees Celsius). This layer contains the ozone layer. Ozone acts as a shield for
in the earth's surface. It absorbs ultraviolet radiation from the sun. This causes a temperature increase
in the upper part of the layer.
Mesophere - 50 to 80 km - in the lower part of the stratosphere. The temperature drops in this layer to about -100 degrees Celsius. This is the coldest region of the atmosphere. This layer protects the earth
from meteoroids. They burn up in this area.
Thermosphere - 80 km and up - The air is very thin. Thermosphere means "heat sphere". The
temperature is very high in this layer because ultraviolet radiation is turned into heat. Temperatures often
reach 2000 degrees Celsius or more. This layer contains:
- Ionosphere - This is the lower part of the thermosphere. It extends from about 80 to 550 km. Gas
particles absorb ultraviolet and X-ray radiation from the sun. The particles of gas become electrically charged (ions). Radio waves are bounced off the ions and reflect waves back to earth. This generally helps
radio communication. However, solar flares can increase the number of ions and can interfere with the
transmission of some radio waves.
- Exosphere - the upper part of the thermosphere. It extends from about 550 km for thousands of
kilometers. Air is very thin here. This is the area where satellites orbit the earth.
Magnetosphere - the area around the earth that extends beyond the atmosphere. The earth's magnetic
field operates here. It begins at about 1000 km. It is made up of positively charged protons and negatively charged electrons. This traps the particles that are given off by the sun.
They are concentrated into belts or layers called the Van Allen radiation belts. The Van Allen belts trap deadly radiation. When large amounts are given off during a solar flare, the particles collide with each other
causing the aurora borealis or the northern lights.
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