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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-14
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-14
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 28 Jan 2019

Regular paper | 28 Jan 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Investigation of the ionospheric absorption response to flare events during the solar cycle 23 as seen by European and South African ionosondes

Veronika Barta1, Gabriella Sátori1, Kitti Alexandra Berényi2,1, Árpád Kis1, and Earle Williams3 Veronika Barta et al.
  • 1Geodetic and Geophysical institute, Research Centre for Astronomy and Earth Sciences, Sopron, Hungary
  • 2Eötvös Loránd University, Budapest, Hungary
  • 3Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, USA

Abstract. Systematic analysis of ionosopheric parameters measured at mid- and low-latitudes was performed to study the ionospheric response to solar flares. The lowest recorded ionosonde echo, the mimimum frequency (fmin, a qualitative proxy for the nondeviative radio wave absorption occurring in the D-layer), furthermore the dfmin parameter (difference between the value of the fmin and the mean fmin for reference days) have been investigated. The time series of the fmin and dfmin parameters recorded at meridionally-distributed ionosonde stations in Europe and South Africa were analyzed during eight X and M class solar flares during solar cycle 23. The solar zenith angles of the observation sites at the time of the selected flares have been also taken into account. Total and partial radio fade-out was experienced at every ionospheric stations during intense solar flares (> M6). The duration of the total radio fade-out varied between 15 and 150 min and it was highly dependent on the solar zenith angle of the ionospheric stations. Furthermore, a solar zenith angle-dependent enhancement of the fmin (2–9 MHz) and dfmin (1–8 MHz) parameters was observed at almost every stations. The fmin and dfmin parameters show an increasing trend with the enhancement of the X-ray flux. Based on the results, the dfmin parameter is a good qualitative measure for the relative variation of the nondeviative absorption especially in the case of the less intense solar flares which do not cause total radio fade-out in the ionosphere (class < M6).

Veronika Barta et al.
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Veronika Barta et al.
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Short summary
The solar flare effects on ionospheric absorption at mid- and low-latitude have been investigated with the systematic analysis of ionosopheric parameters (fmin, dfmin: deviation from the reference days). A solar zenith angle-dependent enhancement of the parameters was detected but the observed values also depended on the flare insensity. The dfmin parameter found as a good qualitative proxy for the relative variation of ionospheric absorption especially during the less intense solar flares.
The solar flare effects on ionospheric absorption at mid- and low-latitude have been...
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