Structure of groups of eigenfrequencies in spectra of geomagnetic pulsations in the nightside magnetosphere

Using a new method of correlation function for amplitude and phase fluctuations (APCF), records of geomagnetic field component fluctuations (observatories Mondy and Borok) have been processed for a number of hour zones of the nightside magnetosphere. This method is meant to detect groups of equidistant frequencies inside the spectrum of source signal and also to measure a difference between two neighbor frequencies in each of these groups. The groups of equidistant frequencies in broadband spectra of these fluctuations are shown to depend on eigenfrequencies of the 2D Alfvén wave resonator, just as for dayside fluctuations [Polyakov, 2018]. An empirical relation has been found between a combination of parameters of this resonator and local time. The similarity between structural elements in the final products of processing of Alfvén fluctuation N-S and E-W components for almost all hour zones clearly indicates the reliability of the results of the APCF method in processing any broadband signals.