Earth-Ionosphere Cavity Resonator - Ultra and Extremely Low Frequency Electromagnetic Fields - page 106

Chapter 4
Earth-Ionosphere Cavity Resonator

Abstract This chapter covers both the global ULF/ELF electromagnetic
resonances and background noises. We choose first to study Schumann resonances
excited in the Earth-Ionosphere cavity resonator by the global lightning activity
treated as stochastic process. In the analysis that follows, we first examine models
of the Earth-Ionosphere cavity and then derive eigenfrequencies of the Schumann
resonances. In this chapter we estimate the contribution of positive and negative
cloud-to-ground (CG) lightning discharges to the low-frequency portion of power
spectra and to the Schumann resonances.

Keywords Earth-Ionosphere cavity resonator ￿ Negative cloud-to-ground (CG)
lightning ￿ Positive CG lightning ￿ Quality/energy-factor ￿ Random lightning
process ￿ Schumann resonances

4.1 Structure and Models of the Earth-Ionosphere

Cavity Resonator

4.1.1 Model of the Earth-Ionosphere Cavity

and Basic Equations

A large fraction of the ground surface is covered by sea water with conductivity
g 5 S/m, while the continental conductivity of the Earth crust varies in the range
g D 10 4 -10 2 S/m. Both of these values are much greater than the atmospheric
conductivity at the sea level. The conductivity of the air increases exponentially
with altitude according to Eq. ( 3.1 ). In the ELF range of 3-30 Hz the displacement
current in the atmosphere is much greater than the conduction one up to the
altitudes 45-50 km. This implies that in the ELF range the lower atmosphere can
be considered as a perfect insulator sandwiched between two conducting layers.