Line splitting in the Schumann resonance oscillations

We discuss detection of line splitting in the global electromagnetic (Schumann) resonances. The lifting of resonance degeneracy is usually not visible in the ordinary power spectrum of either the electric or magnetic field components since splitting is small in comparison with the natural width of the resonance lines. Splitting may be detected by exploiting the spatial structure of the fields and/or the elliptical polarization of the magnetic field. The spatial properties were utilized in synchronous and coherent measurements of the vertical electric field at two longitudinally separated observatories. The results were attributed to line splitting. An alternative interpretation was also advanced that takes into account the source‐receiver separation. The lifting of degeneracy also appears as a frequency‐dependent elliptical polarization of the horizontal magnetic field vector, which has been found experimentally. We compare measurement and computational data, and their reciprocity proves the detection of Schumann resonance line splitting.