The mesosphere and upper atmosphere in the context of TLEs

The mesosphere and upper atmosphere form the environment in which TLEs arise. These are the layers between the storm troposphere and the conductive ionosphere, and it is here that sprites (~40-90 km) and elves (~90 km, at the lower edge of the ionosphere) take place — see #65.

From the standpoint of the electrodynamics of the Earth-ionosphere cavity, this region is important in two ways. On the one hand it delimits the upper wall of the cavity in which the Schumann resonance exists: the height and conductivity profile of the lower ionosphere determine the properties of the resonances. On the other hand it is the stage of the luminous phenomena themselves — TLEs are essentially the link between tropospheric storms and the ionosphere, by which the energy of a lightning discharge is transferred upward and manifests itself both optically and electromagnetically.

The study of TLEs therefore simultaneously sheds light on the state of the upper atmosphere: the optical and ELF manifestations carry information about how the rarefied mesospheric environment reacts to the intense electric field above the storm. In this way cluster I connects with the questions of the lower-ionosphere profile, which are key for the Schumann resonance.