Thermosphere

The thermosphere is the atmospheric region from 85 to 500km altitude, containing the ionosphere. It is characterized by high temperature and large variability, in response to changes in solar ultraviolet radiation and solar-driven geomagnetic activity. The composition of the lower thermosphere is primarily N₂ and O₂, similar to the lower and middle atmosphere, but in the upper thermosphere atomic oxygen (O) becomes the dominant gas, due to the importance of photodissociation and molecular diffusion at high altitude. Thermospheric dynamical motions result from complex interactions between solar heating, auroral processes, the resulting pressure gradients, and dissipative processes.