Fig3_4 Earth's layered atmosphere

Fig3_4 Earth

Fig. 3.4 . The pressure of our atmosphere (right scale) decreases with altitude (left scale). This is because fewer particles are able overcome the Earth’s gravitational pull and reach higher altitudes. The temperature (bottom scale) also decreases steadily with height in the ground-hugging troposphere, but the temperature increases in two higher regions that are heated by the Sun. They are the stratosphere, with its critical ozone layer, and the ionosphere. The stratosphere is mainly heated by ultraviolet radiation from the Sun, and the ionosphere is created and modulated by the Sun’s x-ray and extreme ultraviolet radiation that breaks the atmospheric molecules apart, and strips electrons off their component atoms to produce ions. The process of ionization by the Sun’s invisible rays releases heat to warm the ionosphere, so the temperature rises with altitude in it. In the ionosphere, at about 100 km to 500 km above the ground, the temperatures skyrocket to higher values than anywhere else in the entire atmosphere. At higher altitudes, the atmosphere thins out into the exosphere, or the “exit to the outside sphere.” The temperature is so hot out there, and the particles move so fast, that some atoms and molecules may slowly evaporate away.

Copyright 2010, Professor Kenneth R. Lang, Tufts University