Discharge Processes in a Stratosphere and Mesosphere During a Thunderstorm - The Atmosphere and Ionosphere - page 246

Fig. 5.30 Spectra of radiation: ( a ) spectrum of MW streamer subcritical discharge; ( b ) spectrum
of the “sprites” (Barrington-Leigh 2000 )
In a sufficiently strong thunderstorm, this residual field exceeds the critical value
on the bottom border of the ionosphere. There originates the avalanche of ionization
moving downward with the speed of 10 8 -10 9 cm/s. This is the “elf.”
The front of the avalanche ionization is unstable with respect to the growth
of the asperities with sharpening peaks. The size of the bases of the asperities is
determined by the depth of the avalanche front. When the asperities reach the zone
of the subcritical field, the system of streamer channels appears at the tops of the
asperities, sufficiently thin for development in the deeply subcritical field.
The relaxation time of the electric field is great enough for the development of
the process during tens of milliseconds. The asperities with the attached streamer
channels net are the “sprites.”
Filamentation of the polarization currents at altitudes higher than 120 km creates
the flash of IR radiation. The bright part of the elf and the streamer part of the sprites
generate the flash of UV radiation that is registered by the satellites.
Acknowledgments The author thanks Boris Khrenov, who has attracted his attention to the
most interesting problem of the high-altitude discharges, and the participants of the theoretical
department of General Physics Institute of RAS seminar, headed by Prof. A.A. Rukhadze, for
constructive discussion.