The mesosphere, at 50km to 80-90km altitude above Earth's surface, is directly above which other layer?
Mesosphere for applications such as submillimetre astronomy. High-altitude balloons are often flown by students and by amateur groups to altitudes on the order of , for both scientific and educational purposes. Mesosphere The mesosphere (; from Greek "mesos" "middle" ) is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as the altitude increases. This characteristic is used to define its limits: it begins at the top of the stratosphere (sometimes called the stratopause), and ends at the mesopause, which is the coldest part of Earth's atmosphere with
Sodium layer Sodium layer The sodium layer is a layer of neutral atoms of sodium within Earth's mesosphere. This layer usually lies within an altitude range of above sea level and has a depth of about . The sodium comes from the ablation of meteors. Atmospheric sodium below this layer is normally chemically bound in compounds such as sodium oxide, while the sodium atoms above the layer tend to be ionized. The density varies with season; the average column density (the number of atoms per unit area above any point on the earth's surface) is roughly 4 billion sodium atoms/cm. For a