Geoscience Reference
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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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