Structure of the Atmosphere
Learning Objectives
The atmosphere surrounds Planet Earth providing protection from and distributing the Sun's energy. The atmosphere is dynamic and can be thought of as a thin fluid layer that blankets our planet.
Composition of the atmosphere:
Nitrogen 78%
Oxygen 21%
all other gases 1%
Carbon Dioxide 0.3%
Structure of the Atmosphere:
The atmosphere is divided into 4 layers
1) Troposphere: the bottom layer of the atmosphere, it extends from the surface to approximately 11km. This is where "weather" occurs. As you go up in altitude the air becomes colder. There is lots of vertical and horizontal air movements in this layer.
2) Stratosphere: Relatively stable layer, the air becomes warmer with altitude. The stratosphere extends from 11km to 50km. Vertical air movement is weak but there are strong horizontal movements. The ozone layer is within the stratosphere.
Ozone layer: Incoming solar radiation strikes the atmosphere and splits the oxygen (O2) molecule into two individual oxygen atoms. These individual atoms then react with the remaining O2 molecules to form ozone (O3) molecules. The ozone molecule absorbs ultraviolet radiation from the Sun, essentially shielding our planet from UV radiation. Ultraviolet radiation destroys DNA and life could not exist if the ozone layer were not present. There is some concern about the ozone layer because a hole in the ozone layer opens over Antarctica every year during the Southern Hemisphere spring. Refer to class discussion on ozone problem.
3) Mesosphere: Extending from 50km to 80km the temperature drops with altitude in the mesosphere. The coldest area of the atmosphere is in the Mesosphere at 80km.
4) Thermosphere: This area extends from 80km to 600km and the edges blend with space. The atmosphere warms with altitude.
Ionosphere: located in the upper mesosphere and lower thermosphere, the ionosphere is an area with a high concentration of free ions. The amount of ions present vary with the time of day and the season. The ions form from solar radiation striking oxygen and nitrogen releasing positivly charged ions and free electrons. The ionosphere distorts radio waves either disrupting them or causing them to travel great distances. The ionosphere is also responsible for the Aurora Borealis (Northern Hemisphere) and the Aurora Australis (Southern Hemisphere).
Auroras: The magnetic field that encircles the Earth dips inward at the poles. The magnetic field acts to deflect the solar wind. (The solar wind is a stream of protons and electrons thrown outward from the Sun.) Where the magnetic field dips at the poles the solar wind comes in contact with the ionosphere and the solar wind excites the particles in the ionosphere to higher energy state. This causes the ions to emit radiation in the visible spectrum
(ie glow) forming the Northern and Southern Auroras.
related sites:
Site with information about the Aurora Borealis including pictures and links to other sites. Click Here
