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Investigation of ionosphere response to geomagnetic storms over the propagation paths of very low frequency radio waves
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  • Victor U. J. Nwankwo,
  • Jean-Pierre Raulin,
  • Dra. Emilia Correia,
  • William F. Denig,
  • Olanike Akinola,
  • Olugbenga Ogunmodimu,
  • Rafael R De Oliveira
Victor U. J. Nwankwo
Anchor University

Corresponding Author:[email protected]

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Jean-Pierre Raulin
CRAAM - Universidade Presbiteriana Mackenzie
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Dra. Emilia Correia
Instituto Nacional de Pesquisas Espaciais/CRAAM
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William F. Denig
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Olanike Akinola
Centre For Atmospheric Research, National Space Research and Development Agency, KSU Campus
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Olugbenga Ogunmodimu
Department of Electrical and Electronics Engineering, Manchester Metropolitan University
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Rafael R De Oliveira
Universidade Presbiteriana Mackenzie
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We analysed variations in signal metrics and the diurnal amplitude of VLF radiowaves from four propagation paths during intervals of 4 geomagnetic storms on 17, 26 September, 25 October and 1 November 2011. Three propagation paths are located at mid-latitude in the Northern Hemisphere, and one crossing the equatorial ionospheric anomaly (EIA) crests and magnetic equator. Our results show significant reduction in the mean amplitude before sunrise (MBSR), the daytime mean amplitude (DTMA) and the mean amplitude after sunset (MASS) signal strength in majority of the cases analysed. The ratio of the storm day signal-decrease (SDSD) to the total number of points (TNoPs) considered are 0.7692, 0.9231 and 0.6923 for MBSR, DTMA and MASS, respectively, while the respective ratio of storm day signal-increase (SDSI) to the TNoPs are 0.1538, 0.0769 and 0.3846. Of the four propagation paths, the DHO-A118 path (in the mid-latitude European sector) showed the largest decrease especially during strong storms (that are associated with solar particle events (SPEs)). We also observed distinct anomaly (large signal fluctuation) in NAA-ROI propagation path signal in South-American region (Brazil). We further investigated the state of the ionosphere over the VLF radiowaves propagation paths using the total election content (TEC) obtained from multiple stations near the transmitters and receivers, to understand these propagation characteristics. Data showed larger enhancement of electron density profiles near the DHO transmitter and ROI receiver, suggesting the large signal strength decrease and fluctuation may be related to markedly perturbed ionosphere along the DHO-A118 and NAA-ROI propagation paths.