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Volume 36, issue 5 | Copyright
Ann. Geophys., 36, 1161-1170, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 06 Sep 2018

Regular paper | 06 Sep 2018

Evaluation of the NeQuick model performance under different geomagnetic conditions over South Africa during the ascending phase of the solar cycle (2009–2012)

Sylvain M. Ahoua1,2, John Bosco Habarulema1,3, Olivier K. Obrou2, Pierre J. Cilliers1,4, and Zacharie K. Zaka2 Sylvain M. Ahoua et al.
  • 1South African National Space Agency (SANSA) Space Science Directorate, P.O. Box 32 Hermanus, 7200, South Africa
  • 2Laboratoire de Physique de L'Atmosphère, Université F.H.B. de Cocody, 22 BP 582 Abidjan 22, Côte d'Ivoire
  • 3Department of Physics and Electronics, Rhodes University, Grahamstown, 6140, South Africa
  • 4Department of Electrical Engineering, University of Cape Town, Cape Town, South Africa

Abstract. In order to provide a scientific base to the NeQuick characterisation under disturbed conditions, the comparison of its performance for quiet and storm days is investigated in the southern mid-latitude. This investigation was realised using the two versions of the NeQuick model which were adapted to local and storm-specific response by using the critical frequency of the F2 layer (foF2) and the propagation factor (M(3000)F2) derived from three South African ionosonde measurements, Hermanus (34.40°S, 19.20°E), Grahamstown (33.30°S, 26.50°E) and Louisvale (28.50°S, 21.20°E). The number of free electrons contained within a 1m squared column section known as total electron content (TEC) is a widely used ionospheric parameter to estimate its impact on the radio signal passing through. In this study, the TEC derived from the adapted NeQuick version is compared with observed TEC derived from Global Navigation Satellite System (GNSS) data from co-located or nearby GNSS dual-frequency receivers. The Hermanus K-index is used to select all the disturbed days (K-index ≥ 5) upon moving from low to high solar activity (from 2009 to 2012). For each disturbed day, a quiet reference day of the same month was chosen for the investigation. The study reveals that the NeQuick model shows similar reliability for both magnetic quiet and disturbed conditions, but its accuracy is affected by the solar activity. The model is much better for moderate solar activity epochs (2009 and 2010), while it exhibits a discrepancy with observations during high solar activity epochs. For instance in Hermanus, the difference between GPS TEC and NeQuick TEC (ΔTEC) is generally lower than 10 TECu in 2009, and it sometimes reaches 20 TECu in 2011 and 2012. It is also noticed that NeQuick 2 is more accurate than NeQuick 1, with an improvement in TEC estimation more significant for the high solar activity epochs. The improvement realised in the latest version of NeQuick is more than 15% and sometimes reaches 50%.

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Short summary
Many studies carried out for model validation are realised under geomagnetically quiet conditions. For climatological models this is not an issue. But for models like NeQuick, which plays a crucial role in daily human activities, it has to be evaluated under different conditions. Our study, which is probably a preliminary study, shows the advantage of the ingestion of ionospheric data. Thus, through this technique, a model could be assessed regardless of the geomagnetic activity.
Many studies carried out for model validation are realised under geomagnetically quiet...