Spectral analysis of IAR oscillations to determine the value and variability of the peak electron density NmF2

This methodical paper explores the possibility of estimating the peak electron density of the F2-region of the ionosphere (NmF2) under different conditions, using data on the frequency of spectral bands (harmonics) of the ionospheric Alfvén resonator (IAR) oscillation. We describe a simple technique for tracking the frequency of spectral bands during the day by measuring their position on the plot of the IAR daily dynamic spectrum. Through calculations within the framework of the global ionospheric model IRI-2016, we verify the correctness of the comparison of the frequencies of resonant bands, measured at one point, with data from radio sounding, performed at other points remote from IAR frequency measurement sites at a distance. We propose an algorithm for comparing NmF2, measured by a radiosonde, with frequencies of spectral lines by precalculating the evaluation factor. It is formed on the basis of a nonlinear combination of the frequencies of the three observed harmonics. Then the time series of this factor is compared with the results of radio sounding, and correlation and regression coefficients, as well as estimation errors are calculated. Using the material on rare cases of round-the-clock observation of IAR oscillations in the winter months of 2011–2012, we trace the dependence of the average error in determining the peak electron density on local time. We present the data on the most favorable local time intervals for determining NmF2 from IAR harmonic frequencies depending on season. Some additional factors are discussed which affect the accuracy of estimates and determine the frequency range of IAR oscillations.