Numerical Estimate of the Spectral Resonance Structure Frequency Scale of Natural ULF Magnetic Field

The spectral resonance structure (SRS) of the magnetic component of natural electromagnetic noise in the frequency range 0.5 – 2.5 Hz is investigated to estimate the frequency scale of the structure. The magnetic field data recorded at 49°20'N, 22°40'E, in the Bieszczady Mountains, Poland, at night hours of May 1996 – 2001 are used. It is assumed that the resonant frequency pattern of the ionospheric Alfvén resonance (IAR) appears in the spectral resonance structure. Both a model of the ionospheric Alfvén resonance for night-time conditions of the ionosphere and an algorithm of evaluating the frequency scale are presented. The algorithm is applied to the experimental data. The results are compared to those obtained with the International Reference Ionosphere model.