Spectral analysis of auroral currents

The keograms taken by full survey cameras enable us to find auroral activity cases with quasistationary discrete polar aurorae observed. Geomagnetic-variation data from ground-based magnetometers are used for the spectral analysis of auroral currents in such an event. The spectral analysis is applied to magneto-differential data; i.e., to magnetic field differences measured at neighbouring stations. This approach allows us to isolate a signal of the local ionospheric current and remove signals of distant magnetic-field sources. The spectral analysis is conducted with the numerical measurement processing that includes the discrete Fourier transformation and the filtration by the spectral window. The filtration with the lowest window resolution reveals the spectrum that involves wide power maxima with equidistant dedicated-frequency peaks. The discrete spectrum is evidence of the existence of the auroral current system with a certain structure.