Natural electromagnetic pulses in the ELF range

Abstract

We analyze the propagation of electromagnetic waves in the ELF. We apply the modal solution for the spherical Earth-ionosphere cavity and obtain the time domain fields using the FFT algorithm. The Schumann resonance amplitude over the frequency-distance plane consists of summits and depressions exhibiting separate extended zones. When the source-observer distance is small, the field maximum is found at some hundred herts. This component rapidly decays with the distance. The time domains ELF pulse travels with a constant velocity and 'bounces' from the source antipode. Its width increases along the path due to absorption of the high frequency component. The distance dependence of the pulse amplitude depends on both the geometrical focusing and the high frequency absorption.