Modeled and measured SR frequency data (Ez, NCK, Hungary)

This dataset contains modelled and measured SR frequency data. 

Files prepared by Tamás Bozóki (25 April, 2024)Contact: [e-mail]

model_f1.txt, model_f2.txt, modef_f3.txt

The modelled data have been prepared based on the open-source python package called “schupy”, which enables calculating theoretical SR spectra for arbitrary source-observer configurations (Bozóki et al., 2019). The model applies the solution of the 2-D telegraph equation for the uniform Earth-ionosphere cavity (see e.g., Prácser et al., 2019) characterized by two complex, frequency-dependent altitudes (He/Hm representing the electric and magnetic altitudes, respectively, see Mushtak & Williams, 2002 for more details), and is capable of modeling extended sources represented by randomly distributed point sources within the given radius from the center of the source (100 point sources are distributed in this case). For the present dataset, simulations were performed with source radii of 1.5, 1.8, 2.0 and 3.0 Mm, and theoretical SR spectra were calculated with a frequency resolution of 0.1 Hz between 1 and 48 Hz. In terms of the source-observer distance, we covered the range from 20 to 140 degrees with a resolution of 0.5 degrees. In order to extract modal peak frequencies corresponding to the first three SR modes, after applying a quadratic interpolation on the spectra to increase the frequency resolution to 0.01 Hz, we looked for spectral peaks in the following bands: f1: 6-10 Hz, f2: 11-16 Hz, f3: 18-22 Hz.

NCK_f1_1994-2014.txt, NCK_f1_1996_03_01-06.txt, NCK_f1_2023_02_01-28.txt, NCK_f2_1994-2009.txt, NCK_f2_2023_02_01-28.txt, NCK_f3_2000-2009.txt, NCK_f3_2023_02_01-28.txt

SR frequencies and amplitudes of the first three modes (~ 8 Hz, ~14 Hz, ~20 Hz) of the EZ field component have been recorded at the Széchenyi István Geophysical Observatory, also known as the Nagycenk Geophysical observatory (NCK; 47.6°N, 16.7°E) in Hungary, Central Europe since May 1993 using a very stable ball antenna, a preamplifier with high input impedance and a low noise amplifier, and a personal computer with high speed, multi-channel A-to-D-converter (Sátori et al., 1996). The complex demodulation has been applied as a spectral technique which is very suitable to examine the time variation of the phase and amplitude of selected frequency components in a time series. These parameters of the complex wave vector are determined in time intervals corresponding to the central period of a pre-selected frequency range. By computing the phase change versus time the frequency can be monitored in time. Using this spectral technique the SR peak frequencies are determined in the frequency range of the first three SR modes, namely in the respective ranges: 7-9 Hz, 13-15 Hz and 19-21 Hz. The method was tested with observations (Sátori et al., 1996; Sátori, 1996). Under locally undisturbed conditions, 52 (60 from the year of 2020) time windows of 35.8 sec each are evaluated in one hour while altering the sampling and filtering processes. The number of filtered complex wave vectors is 298, 512 and 716 for the 1st, 2nd and 3rd modes, respectively, in a time window in an optimum case (all amplitudes are accepted) which assures the high accuracy of the estimated frequency values. The standard deviations of the hourly frequency averages are ±0.008-0.012 Hz for the first mode, ± 0.010-0.018 Hz for the second mode and ± 0.016-0.030 Hz for the third mode under locally undisturbed conditions in the vicinity of the SR ball antenna at NCK. 

Acknowledgements

This contribution was supported by the National Research, Development, and Innovation Office, Hungary-NKFIH, project numbers K138824 (G.S., T.B., E.P.) and PD146019 (T.B.).

References:

Bozóki, T., Prácser, E., Sátori, G., Dálya, G., Kapás, K., & Takátsy, J. (2019). Modeling Schumann resonances with schupy. J. Atmos. Sol. Terr. Phys., 196. https://doi.org/10.1016/j.jastp.2019.105144

Mushtak, V. C., & Williams, E. R. (2002). ELF propagation parameters for uniform models of the Earth-ionosphere waveguide. J. Atmos. Sol. Terr. Phys., 64(18), 1989–2001. https://doi.org/10.1016/S1364‐6826(02)00222‐5

Prácser, E., Bozóki, T., Sátori, G., Williams, E., Guha, A., & Yu, H. (2019). Reconstruction of global lightning activity based on Schumann resonance measurements: Model description and synthetic tests. Radio Sci., 54(3), 254–267. https://doi.org/10.1029/2018RS006772 

Sátori, G. (1996). Monitoring Schumann resonances-II. Daily and seasonal frequency variations. J. Atmos. Terr. Phys., 58(13), 1483–1488. https://doi.org/10.1016/0021-9169(95)00146-8 

Sátori, G., Szendrői, J., & Verő, J. (1996). Monitoring Schumann resonances—I. Methodology. J. Atmos. Terr. Phys., 58(13), 1475–1481. https://doi.org/10.1016/0021-9169(95)00145-X