Preprints
https://doi.org/10.5194/angeo-2021-42
https://doi.org/10.5194/angeo-2021-42

  06 Aug 2021

06 Aug 2021

Review status: this preprint is currently under review for the journal ANGEO.

Diagnostic study of geomagnetic storm-induced ionospheric changes over VLF signal propagation paths in mid-latitude D-region

Victor U. J. Nwankwo1, Sandip K. Chakrabarti2, William Denig3, Olugbenga Ogunmudimu4, Muyiwa P. Ajakaiye1, and Paul I. Anekwe1 Victor U. J. Nwankwo et al.
  • 1Space, Atmospheric and Radiowave Propagation Laboratory, Department of Physics, Anchor University, Lagos, Nigeria
  • 2Indian Centre for Space Physics, Kolkata-700084, India
  • 3St. Joseph College of Maine, Standish, ME 04084, U.S.A
  • 4Department of Electrical Engineering, Manchester Metropolitan University, Manchester, UK

Abstract. We performed a diagnostic study of geomagnetic storm-induced disturbances that are coupled to the lower ionosphere in mid-latitude D-region using propagation characteristics of VLF radio signals. We characterised the diurnal VLF amplitude (from two propagation paths) into five metrics, namely the mean amplitude before sunrise (MBSR), midday amplitude peak (MDP), mean amplitude after sunset (MASS), sunrise terminator (SRT) and sunset terminator (SST). We analysed and monitored the trend in variations of signal metrics for up to 20 storms, to understand deviations in the signal that are attributable to the storms; five storms (and their effects on the signals) were studied in detail, followed by statistical analysis that included 15 other events. Considering the quietient pre-day level following the storm our results showed that the MDP exhibited characteristic dipping in about 67 % and 80 % of the events for GQD-A118 and DHO-A118 propagation paths, respectively. The MBSR showed respective dipping of about 77 % and 60 %, while the MASS dipped by 58 % and 67 %. Conversely, the SRT and SST showed respective dipping of 25 % and 33 %, and 42 % and 47 %. Of the two propagation paths used in this study, the dipping of the amplitude of DHO-A118 propagation path signal is larger (as also observed in previous study). To understand the state of the ionosphere over the signal propagation paths and how it affects the VLF responses, we further analysed virtual heights (h'E, h'F1 and h'F2) and critical frequencies (foE, foF1, and foF2) of the E and F regions (from ionosonde stations near the transmitters). The results of this analysis showed a significant increase and/or fluctuations of the foF2, foF1, h'F2, h'F, h'Es and h'E near both transmitters during the geomagnetic storms. The largest increase in heights of the regions (h'F2, h'F, h'Es and h'E) occured over Juluisruh station (around the DHO transmitter) in Germany, suggesting a strong storm responses over the region leading to the large dipping of the DHO-A118 propagation path signal.

Victor U. J. Nwankwo et al.

Status: open (until 06 Oct 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on angeo-2021-42', Sergey Sokolov, 07 Sep 2021 reply

Victor U. J. Nwankwo et al.

Victor U. J. Nwankwo et al.

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Short summary
We characterised the diurnal VLF amplitude into five metrics – mean amplitude before sunrise (MBSR), midday amplitude peak (MDP), mean amplitude after sunset (MASS), sunrise terminator (SRT) and sunset terminator (SST). We analysed their trend in variations of the signal during geomagnetic storms and found that the signal exhibit significant dipping due to the storms. Responses of high frequency radio pulses also showed evidence of markedly disturbed ionosphere over the signal paths.