Geoscience Reference
In-Depth Information
K
a
(
E/N
), and ionization by the electron impact
K
i
(
E/N
) reactions and the coeffi-
cients of the ion-ion ˇ
i
and the ion-electron ˇ
e
recombination, are taken for the air
mixture:
8
<
@t
D
K
a
E
N.
z
/n
e
ˇ
i
n
n
C
;
@n
N.
z
/
@t
D
K
i
E
N.
z
/n
e
ˇ
e
n
e
n
C
C
‰.
z
/;
@n
C
N.
z
/
(5.24)
:
n
e
D
n
C
n
;
@E
@t
D
4
tot
.
z
/E
C
@E
cloud
.
z
;t/
@t
:
where
tot
(
z
) is defined by Eqs.
5.14
and
5.13
.
The field of the cloud itself first rises during its charging up to the moment of
time
t
0
, after which the lightning channel connects the cloud with ground. The
resonant counter, formed by cloud capacity and lightning channel inductivity, starts
the damping oscillations at the law given by Eq.
5.25
:
8
<
1
e
ch
; if t<t
0
cos..t
t
0
//e
ı.tt
0
/
; if t>t
0
t
E
cloud
.
z
;t/
D
E
cloud
.
z
/
:
(5.25)
:
Here
c
L
c
r
ln
2h
0
(5.26)
a
ld
In the frequency of the contour, determined by geometric parameters of the model
(see Fig.
5.14
),
a
ld
is the lightning channel radius,
c
is the light velocity, and • is the
decay factor of oscillations caused by finite conductivity of the lightning channel.
The decay factor is chosen equal to 0.4. Dependencies of the electric field of the
cloud (Fig.
5.22
a) and the current in the lightning channel (Fig.
5.22
b) are shown
at
t
>
t
0
.
Results of the modeling are shown in Fig.
5.23
.
As one can see, the layer of ionization, which is retained for a long time under the
bottom border of the ionosphere, appears during the time of the lightning discharge.
The electric field inside the arisen layer is small, so the dissociative attachment
ceases to play an appreciable role. The three-body attachment also is insignificant,
as the concentration of molecules is small at the altitudes of the generation of the
ionization layer. The layer lifetime is defined by the recombination and is as long
as hours. Occurrence of the ionization layer has the character of an avalanche of
ionization, which moves downward with a speed about of 10
8
cm/s, until it does
not reach the border of the overcriticality region. The arisen layer of the ionization
