The atmospheric layer between the mesosphere and the exosphere.
Region of the Earth's atmosphere beyond about 50 miles/80 km above the surface, in which the temperature steadily increases with height.
Layer in the Earth's atmosphere above the mesosphere and below the exosphere. Its lower level is about 80 km/50 mi above the ground, but its upper level is undefined. The ionosphere is located in the thermosphere. In the thermosphere the temperature rises with increasing height to several thousand degrees Celsius. However, because of the thinness of the air, very little heat is actually present.