Thermosphere gas and the ionospheric plasma. The International Space Station orbits the Earth within the middle of the thermosphere, between . It is convenient to separate the atmospheric regions according to the two temperature minima at about 12 km altitude (the tropopause) and at about 85 km (the mesopause) (Figure 1). The thermosphere (or the upper atmosphere) is the height region above 85 km, while the region between the tropopause and the mesopause is the middle atmosphere (stratosphere and mesosphere) where absorption of solar UV radiation generates the temperature maximum near 45 km altitude and causes the ozone layer. The density
Atmosphere of Uranus spots and noticeable seasonal changes. (see below) The stratosphere is the middle layer of the Uranian atmosphere, in which temperature generally increases with altitude from 53 K in the tropopause to between 800 and 850 K at the base thermosphere. The heating of the stratosphere is caused by the downward heat conduction from the hot thermosphere as well as by absorption of solar UV and IR radiation by methane and the complex hydrocarbons formed as a result of methane photolysis. The methane enters the stratosphere through the cold tropopause, where its mixing ratio relative to molecular hydrogen is about 3,