Graphical Schemes Designed to Display and Study the Long-term Variations of Schumann Resonance

This work proposes and illustrates a graphical approach aimed at studying a wide range of features of the ELF horizontal magnetic field signal recorded at the Sierra Nevada station (Spain). In addition to the traditional long-term variations in the parameters of the first three Schumann resonances (their amplitudes, central frequencies and widths), many other properties such as the saturations of the magnetometers, anomalous values for the parameters or spectra with any kind of particularities are taken into consideration in this work. These features can provide us with complementary information about the long-term variation of Schumann resonances, give an estimation of the extent up to which the results obtained are reliable and be correlated with the occurrence of lightning events or with changes in the electrical properties of the ionosphere. The scheme proposed in this work allows to instantaneously display the variations of all these features within a desired period of time.