This paper considers theoretically the n = 1 and 2 Schumann resonances of the Earth-ionosphere cavity, in particular the power contained in the vertical electric field and the horizontal magnetic field at different distances from the lightning (considered to be vertical dipoles) which excites the cavity. A relative minimum of the fields is found at a distance of ~ 10,000 km, one quarter of the Earth's circumference. The longitudinal size (breadth) of the source region, in hours, is also considered.

Section 3 uses this theory to calibrate horizontal magnetic field measurements made at the Akademik Vernadsky station in Antarctica. There is the potential to use this theory for other Schumann resonance receiving stations around the world.

Fig. A1 presents the global average vertical profile of atmospheric electric conductivity (in S/m) for ground level up to an altitude of 110 km that is used in the calculations. The right-hand panels of Fig. A2 show the frequency dependence of the real and imaginary parts of the complex propagation constant nu(f) at these extremely low frequencies.

The paper contains a useful set of references for readers.