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Fig. 3.4
Model calculations of thunderstorm quasielectrostatic (QE) field preceding a conven-
tional
CG stroke. The vertical electrical field profile along z -axis as a function of altitude z is
shown with solid line. The fields required for the propagation of negative and positive streamers in
the air are shown with dash lines 1 and 2, respectively. A runaway breakdown field is shown with
dash line 3. The numerical values of parameters are assumed to be typical for the generation of
CG strokes (Surkov and Hayakawa 2012 )
gas temperature the value of E c is proportional to number density n m of the neutral
gas. Taking into account of Eq. ( 2.3 )forn m we thus obtain that the conventional
breakdown threshold falls off approximately exponentially with altitude
E c D E 0 exp . z =H a /:
(3.5)
Here E 0 32 kV/m is the constant of the order of breakdown threshold at the
ground level.
As the electric field exceeds the breakdown threshold ( 3.5 ), the streamer
mechanism of air breakdown may develop (e.g., see Bazelyan and Raizer 1998 ).
A typical streamer is the self-propagating narrow filament of cold low-conducting
plasma which can propagate at the velocity 10 2 -10 4 km/s as measured at the
ground pressure. The electric field in the vicinity of the streamer head can be
about 4-7 times larger than E c due to the high charge density at streamer head.
This results in the electron impact- and photo-ionization in the streamer head
followed by an enhancement of ionization coefficient up to the value occurring at
the streamer channel (e.g., Raizer et al. 1998 ;Pasko 2006 ; Celestin and Pasko 2010 ).
In laboratory experiments such as point-to-plane corona discharges, the individual
electron avalanches initiate the streamer in the vicinity of the sharp portion of an
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