Simultaneous observations of Schumann resonances in California and Australia: Evidence for intensity modulation by the local height of the D region

Observations are presented of the horizontal magnetic component of Schumann resonance intensities as simultaneously measured at locations in California and Western Australia during two separate intervals September 2-17, 1989, and April 14-21, 1990. For both intervals, diurnal variations of the average magnetic power over the lowest three modes of the Schumann resonances showed substantially different temporal profiles at the California and Western Australia stations, with interstation correlations of 0.51 and 0.39, respectively. A method is demonstrated for determining from these observations the average local time variation of the height of the D region. A height variation is obtained that is nearly identical for the respective analysis intervals, with a minimum height occurring at approximately 1300-1400 LT and a maximum-to-minimum height difference of roughly 50% of the mean. When corrected for the local D region height, the detailed diurnal intensity profiles over the analysis intervals display a greatly improved similarity, with interstation correlation coefficients increasing from 0.51 to 0.70 and from 0.39 to 0.82, respectively. Substantial agreement between the two stations after correction for D region height suggest that such observations could be used to monitor the global totality and variability of lightning, quantitatively and at time resolutions of the order of 10 min or less, in studies of global change