Low-frequency (ELF�VLF) radio atmospherics study at the Ukrainian Antarctic Akademik Vernadsky station

Швец, А. В.; Nickolaenko, A. P.; Koloskov, A. V.; Yampolsky, Yu.; Budanov, O. V.; Shvets, A. N.

doi:10.33275/1727-7485.1(18).2019.136

Cited by 7 publications

(2 citation statements)

References 43 publications

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“…The UAS "Akademik Vernadsky" is located near the polar circle, at 65°14´44" S, 64°15´28" W, geomagnetic coordinates at 2019 are 55.7°S and 6.3°E. The receiving unit and the details of its operation were described in (Shvets et al, 2019). Tweeks are observed when the receiving station is in the night hemisphere, e.i.…”

Section: Data and Processing Methodsmentioning

confidence: 99%

Correlational Analysis of the ELF – VLF Nighttime Atmospherics Parameters

Gorishnya

Shvets

2022

UJRS

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Tweek-atmospherics (tweeks), along with radio transmission by VLF radio stations, are used to study the lower ionosphere. Electromagnetic pulse radiation, which has been excited by the lightning discharges, has a maximum spectral density at extra low frequencies range (ELF, 300...3000 Hz) and very low frequencies (VLF, 3...30 kHz). The Earth-ionosphere cavity serves as a waveguide for electromagnetic waves in these frequency ranges. On the spectrogram of the tweek, the initial part is a linearly polarized broadband signal, and then a number of individual harmonics are observed. Their instantaneous frequencies decrease, asymptotically approaching approximately multiples of the cutoff frequencies of the waveguide. The single position method for lightning location and estimation of the ELF wave’s reflection heights in the lower ionosphere by tweeks has been implemented into the computational algorithm. The clusters with approximately the same azimuths and distances to sources which have been obtained during the same night have been identified upon the ensemble of tweek-atmospheric records. The data were accumulated at the Ukrainian Antarctic Station "Akademik Vernadsky" in 2019. The location of the receiving complex in the near-polar region makes it possible to register tweek sources in two world thunderstorm centers with geographic azimuths from –60° to 130°. The results of processing these data have been used by studying the correlation matrix and partial correlation coefficients to identify causal relationships between the three main parameters of the tweek, such as (1) the average azimuth of the arrival of tweeks in regard to the magnetic meridian, (2) the average distance to the center of the cluster of tweek sources (lightning discharges), and (3) the average number of tweek harmonics. The same correlation analysis was applied to two groups with distances to sources of 2.2...7.5 Mm and 7.6...9.5 Mm used for study in detail. It is shown that the partial correlation coefficients between the number of tweek harmonics and the difference of the magnetic azimuth from the magnetic east are 0.624 (for the entire range of distances), 0.696 (for far tweek sources) and 0.595 (for main middle range), so, they always exceed the values of 0.1% significance level. The correlation of tweek spectrum with the distance to the tweek source in the range of 2.2…7.5 Mm has been shown to be comparable in magnitude or to exceed the correlation of tweek spectrum with the magnetic azimuth. The elimination of this masking effect by calculating the partial correlation coefficients made it possible to reveal the magnetic azimuth dependences of the tweek spectra if tweek propagates in a region outside the geomagnetic equator. Thus, the effect of non-reciprocity of propagation of ELF – VLF waves in regard to the magnetic meridian in the east – west and west – east directions is found in the spectra of tweek-atmospherics. It results in an increased probability of detecting tweeks with higher harmonics if their directions of arrival are close to the geomagnetic east. It is also shown that this effect, as a result of increased attenuation during the propagation of ELF – VLF radiation from the west and weakened attenuation during propagation from the east, leads to a highly significant correlation (with probability level more than 99.9%) between the magnetic azimuths of tweeks and the lengths of their paths to the receiving station.

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Section: Data and Processing Methodsmentioning

confidence: 99%

Correlational Analysis of the ELF – VLF Nighttime Atmospherics Parameters

Gorishnya

Shvets

2022

UJRS

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“…The amplitude of Q-bursts exceeds the background ELF sig-nal five and more times, making it possible to analyze them as separate events. Direction finding of Q-bursts is used for location of high-power lightning discharges over the world by single-site (Burke & Jones, 1992;Shvets et al, 2019) and multisite methods (Füllekrug А. Shvets, О. Budanov, О. Koloskov et al: Evaluation of Q-bursts' sources azimuth errors ISSN 1727-7485. Український антарктичний журнал, 2021, № 2, https://doi.org/10.33275/1727-7485.2.2021.677 kov et al, 2004Litvinenko & Yampolsky, 2005;Sato et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Evaluation of errors in estimating the azimuth of powerful lightning discharges from measurements of Q-burstst

Shvets

Budanov

Koloskov

et al. 2021

UAJ

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In this work, we study the variability of errors in determining the azimuth of Q-bursts’ sources on a daily time scale. Qbursts are electromagnetic pulse radiation in the extremely low frequency (ELF) range, excited by powerful lightning discharges, and they are used to locate lightnings over the world. We estimated the errors from data collected for two horizontal orthogonal magnetic field components of Q-bursts. Experimental records of Q-bursts were made at Akademik Vernadsky station from March to April 2019, which covers the vernal equinox day. We determined the azimuth of a Q-bursts’ source by digital rotation of the coordinate system until the signal in one magnetic component would drop to its minimum value. The absolute value of the azimuth error was estimated from the ratio of the Q-burst’s amplitude to the standard deviation of the residual signal. With an automated processing procedure, we analyzed over 800 thousand Q-bursts with amplitude over 10 picotesla. A characteristic diurnal pattern has been discovered in the estimated azimuth errors variations. The night level of the azimuth error exceeded the day level by about two degrees on average. The decrease-rise-decrease И-shaped swing during transition from night to day and mirror-symmetric Nshaped swing during transition from day to night were identified. Each of those transitional swings takes about four hours. A comparison of the daily variations in the total intensity of ELF background noise with the estimated daily azimuth error diagrams demonstrates the opposite character: maximal level of the ELF background noise was observed during the daytime while the estimated azimuth errors take minimal values at this time. This contradicts the generally accepted notion that increasing the noise increases the error. Thus, we suppose that the residual magnetic component in a Q-burst occurs not only from the background noise but can also result from nonlinear polarization of the incident wave due to gyrotropy of the nighttime lower ionosphere. Coherent waves resulting from diffraction of the incident field on the day-night interface in the Earth-ionosphere cavity could explain the И- and N-shaped swings of the azimuth error during the passage of the solar terminator.

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