Earth-Ionosphere Cavity Resonator - Ultra and Extremely Low Frequency Electromagnetic Fields - page 129

Fig. 4.4 Typical average 3-h power spectra of the vertical electric and horizontal magnetic
components over the passband from 3 to 57 Hz. The Schumann resonances were recorded in
the measurements at Table Mountain, California during intervals of diurnal maximum intensity
(1;300-1;600 UT) and minimum intensity (0300-0600 UT). Taken from Sentman ( 1995 )
global lightning activity (e.g., Clayton and Polk 1974 ). In spite of global character
of the Schumann resonances excited by the totality of global lightning, the striking
difference may occur between the diurnal spectra simultaneously recorded at widely
separated locations. Sentman and Fraser ( 1991 ) have demonstrated such a difference
between diurnal profiles recorded in California and Western Australia (distance
about 14;800 km) during 8-day interval in April 1990. It has been hypothesized that