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Fig. 3.9 Model calculation
of current moment of a
multiple return stroke versus
time
30
25
20
15
10
5
0
0
20
40
60
80
100
t , ms
Fig. 3.10 Model calculation
of the absolute value of
current moment spectrum of
multiple return strokes
0.1
0.08
0.06
0.04
0.02
0
0
20
40
60
80
100
f , Hz
3.1.6
Global Thunderstorm Activity
Considering that there are perhaps 2;000 thunderstorms in progress around the
world at any time, the measurements show that slow diurnal variations of the Earth
electric field are in a good agreement with the variations of the global thunderstorm
activity. Worldwide, both the Earth field and thunderstorm activity vary within
˙ 15 % and reach the peak value approximately at the same period from 14 UT till
20 UT. In particular, the diurnal variations of the Earth electric field correlate with
diurnal variation of the global thunderstorm activity (e.g., see Bering et al. 1998 ;
Füllekrug et al. 1999 ; Rycroft et al. 2000 ).
The weather condition and climate peculiarities may greatly affect the distribu-
tion of lightning discharges over the Earth surface. The thunderstorm cells more
 
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