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Strong influence of solar X-ray flares on low-frequency electromagnetic signals in middle latitudes

Version 2 2024-06-05, 01:41
Version 1 2020-09-25, 12:57
journal contribution
posted on 2024-06-05, 01:41 authored by A Rozhnoi, M Solovieva, V Fedun, P Gallagher, J McCauley, MY Boudjada, Sergiy ShelyagSergiy Shelyag, HU Eichelberger
Abstract. In this paper we analysed Sudden Phase Anomalies (SPAs) of VLF/LF signals recorded at Graz (Austria), Birr (Ireland) and Moscow (Russia) stations during two strong solar flares in September 2017. The first X-class 9.3 flare occurred on 6 September at 12:02 UT and the second X-class 8.2 flare was observed on 10 September 2017 at 16:06 UT. Data from seven transmitters in a frequency range between 20–45 kHz are used for the analysis. The SPAs were observed in all middle-latitudes paths (differently orientated) with path lengths from 350 km to 7000 km. Solar X-ray burst data were taken from GOES satellite observations in the wavelength band of 0.05–0.4 nm. If was found that (i) the amplitude of SPAs in different paths varies from 10 to 282 degrees, and (ii) the correlation between the amplitudes of SPAs, the lengths of paths and the signal frequency is weak. The change in effective height of reflection due to lowering of the reflecting layer during the flares was found to be about 12 km for the first event and about 9 km for the second event. Spectral analysis of the X-ray and LF data, filtered in the range between 5 s and 16 min, showed that the LF signal spectra are very similar to X-ray spectra. Maxima of both X-ray and LF spectra are in 2–16 min interval.

History

Journal

Annales of Geophysical

Volume

37

Article number

37

Pagination

843-850

Location

Bologna, Italy

ISSN

1593-5213

Language

English

Publication classification

CN Other journal article

Issue

5

Publisher

Editrice Compositori

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