UpperAtmosphere

The upper atmosphere is the portion of Earth’s atmosphere that lies above the stratosphere. It includes the mesosphere, thermosphere, and exosphere, with altitude ranges commonly described as roughly 50 to 85 kilometers for the mesosphere, 85 to several hundred kilometers for the thermosphere (extending to about 600–1,000 kilometers depending on solar activity), and from around several hundred up to 10,000 kilometers for the exosphere. This region is characterized by extremely low air density and by the interaction of the atmosphere with solar radiation and the space environment.

In the mesosphere, temperatures generally fall with height, making it the coldest layer of the atmosphere. The thermosphere experiences a rise in temperature with altitude due to absorption of extreme ultraviolet and X-ray radiation by molecular and atomic species, potentially reaching several hundred to over a thousand degrees Celsius in sunlit regions, though the air is so thin that heat would be felt minimally. The exosphere marks the gradual transition from atmospheric particles to space, where particles may follow ballistic or escape trajectories. The upper atmosphere contains significant ionization, particularly in the ionosphere, a region that overlaps the thermosphere and exosphere and is important for radio communication and satellite navigation.

Key phenomena associated with the upper atmosphere include auroras, high-altitude winds, and atmospheric drag on spacecraft. Measurements come from satellites, sounding rockets, and ground-based facilities such as incoherent scatter radars and satellite-based remote sensing. The upper atmosphere responds to solar activity and space weather, influencing communication systems and satellite operations.