The air at an altitude of 50 km is one-thousandth as dense as that at Earth’s surface. Moreover, the density of Earth’s atmosphere decreases exponentially with height, so the upper atmosphere—the region between 50 and 1500 km above the surface—includes less than 1% of the total atmospheric mass. Nonetheless, the upper atmosphere is a buffer against the harsh conditions of space, able to absorb energetic particles and solar radiation even more biologically damaging than that which the lower-lying ozone layer intercepts. As a partially ionized plasma, the upper atmosphere interacts strongly with radio signals that are beamed through it to communicate with orbiting satellites. When the plasma is turbulent, for example, global positioning system signals can become unusable. Beyond the upper atmosphere is space, including the magnetosphere, where the solar wind interacts with Earth’s magnetic field. Many of the processes that govern the lower atmosphere have prominent roles in the...
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1 December 2008
December 01 2008
A physicist’s tour of the upper atmosphere
The character of Earth’s upper atmosphere is shaped not only by internal processes but also by energy received from deep space above and Earth’s surface below.
Physics Today 61 (12), 70–71 (2008);