Editing Thermosphere (section)

===Atmospheric waves===
Two kinds of large-scale atmospheric waves within the lower atmosphere exist: internal waves with finite vertical wavelengths which can transport wave energy upward, and external waves with infinitely large wavelengths that cannot transport wave energy.<ref name=VollandTP>Volland, H., "Atmospheric Tidal and Planetary Waves", Kluwer, Dordrecht, 1988</ref> [[Atmospheric gravity wave]]s and most of the [[atmospheric tides]] generated within the troposphere belong to the internal waves. Their density amplitudes increase exponentially with height so that at the mesopause these waves become turbulent and their energy is dissipated (similar to breaking of ocean waves at the coast), thus contributing to the heating of the thermosphere by about 250&nbsp; K in eq.(2). On the other hand, the fundamental diurnal tide labeled (1, −2) which is most efficiently excited by [[solar irradiance]] is an external wave and plays only a marginal role within the lower and middle atmosphere. However, at thermospheric altitudes, it becomes the predominant wave. It drives the electric Sq-current within the [[ionospheric dynamo region]] between about 100 and 200&nbsp; km height.

Heating, predominately by tidal waves, occurs mainly at lower and middle latitudes. The variability of this heating depends on the meteorological conditions within the troposphere and middle atmosphere, and may not exceed about 50%.