Earth-Ionosphere Cavity Resonator - Ultra and Extremely Low Frequency Electromagnetic Fields - page 127

and C CG lightning. To compare the contribution to the global lightning spectrum
due to C CG lightning with that due to CG, we first consider a certain thunderstorm
center. In this case all the lightning is assumed to have the same propagation factor
g and the same arrival angle ' so that the amplitude of the power spectrum given

by Eqs. ( 4.47 ) and ( 4.48 ) can be estimated as j j ǝ M 2 Ǜ j F j

2 . Whence it follows

that (Surkov and Hayakawa 2010 )

n ǝ M n Ǜ j F n j

2
p D M p E LJ LJ F p LJ LJ

n I n ! p l n
p I p ! n l p

j n j
LJ LJ p LJ LJ

2

; (4.51)

where I n =! n D I 3 =! 3 C I 4 =! 4 , and the subscripts n and p stand for the CG and
C CG lightning, correspondingly. The same equation can serve as a rough estimate

of the ratio j n j = LJ LJ p LJ LJ as the global lightning activity is considered.
On account of about an order-of-magnitude dominance in occurrence rate of
negative discharges over positive ones we can estimate a ratio between global
positive and global negative mean frequencies of the strokes as p = n 0:05
(Shalimov and Bösinger 2008 ). As we have noted above, the numerical values
of other parameters are as follows: I p =! p 25-100 C, I n =! n 5:6 C, and
l n l p . Substituting the above numerical parameters of the global CG lightning

into Eq. ( 4.51 ) yields j n j = LJ LJ p LJ LJ .0:06-1/.
This numerical estimate has shown that the C CG lightning can make a consid-
erable contribution to the low-frequency part of the background spectra provided
by the global lightning activity. Furthermore this contribution can be even greater
than that due to CG lightning in spite of the infrequent occurrence of the C CG
compared to the CG lightning. This also implies that C CG lightning can play
a crucial role in the generation of Schumann resonances (Surkov and Hayakawa
2010 ).
Before discussing this, we must point out that the above estimate of Eq. ( 4.51 )
basically depends on the parameters of the CCs which greatly affect the low-
frequency part of the lightning spectra. Taking into account that the CCs carry the
negative/positive charge of the order of q n D I n =! n or q p D I p =! p , we can
reduce Eq. ( 4.51 )to

n .q n l n / 2
p q p l p 2 ;

j n j

LJ LJ p LJ LJ

(4.52)

where the parameters q n l n and q p l p play a role of mean value of the charge moment
change due to the CC. As we have noted above, the positive CC typically transfers
the total charge as high as q p 25-100 C(Rakov 2003 ), an order of magnitude
greater than that due to the negative CC, that results in q p l p q n l n . Although
the flash rate n p , the parameters of global lightning are such that j n j may

be even smaller than that of LJ LJ p LJ LJ .