Abstract
This chapter is concerned with the Earth’s Schumann resonances (SR) and their application to understanding global lightning. The natural electromagnetic waves in the SR frequency range (5 Hz to approx. 60 Hz) radiated by lightning discharges are contained by the Earth-ionosphere cavity. This cavity excitation by lightning can occur as a single energetic flash (a ‘Q-burst’), or as an integration of a large number of less energetic flashes (the ‘background’ resonances). In principle, continuous observations of SR parameters (modal amplitudes, frequencies, and quality factors) provide invaluable information for monitoring the worldwide lightning activity from a single SR station. Relationships between the variation of SR intensity and global lightning activity are shown. Connections between the change of diurnal modal SR frequency range and the areal variation of worldwide lightning are demonstrated. The temporal variation of the diurnal SR frequency patterns characteristic of the global lightning dynamics is also presented. Distortions of ELF waves propagating between the lightning sources and the observer are theoretically discussed based on the TDTE (two-dimensional telegraph equation) technique, focusing on the role of the day-night asymmetry of the Earth-ionosphere cavity. Theoretical and observational results are compared. Both instruments for SR observations and spectral methods for deducing SR parameters are reviewed. Experimental findings by SR on global lightning variations on different time scales (diurnal, seasonal, intraseasonal, annual, semiannual, interannual, 5-day, long-term) are summarized. The growing use of SR measurements as a natural diagnostic for global climate change is emphasized.
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