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. In order to provide a scientific base to the NeQuick characterisation underdisturbed conditions, the comparison of its performance for quiet and stormdays is investigated in the southern mid-latitude. This investigation wasrealised using the two versions of the NeQuick model which were adapted tolocal and storm-specific response by using the critical frequency of the F2layer (foF2) and the propagation factor ( M (3000)F2) derived fromthree South African ionosonde measurements, Hermanus (34.40 ∘  S,19.20 ∘  E), Grahamstown (33.30 ∘  S, 26.50 ∘  E) andLouisvale (28.50 ∘  S, 21.20 ∘  E). The number of freeelectrons contained within a 1 m squared column section known as totalelectron content (TEC) is awidely used ionospheric parameter to estimate its impact on the radio signalpassing through. In this study, the TEC derived from the adapted NeQuickversion is compared with observed TEC derived from Global NavigationSatellite System (GNSS) data from co-located or nearby GNSS dual-frequencyreceivers. The Hermanus K -index is used to select all the disturbed days( K -index  ≥  5) upon moving from low to high solar activity (from 2009to 2012). For each disturbed day, a quiet reference day of the same month waschosen for the investigation. The study reveals that the NeQuick model showssimilar reliability for both magnetic quiet and disturbed conditions, but itsaccuracy is affected by the solar activity. The model is much better formoderate solar activity epochs (2009 and 2010), while it exhibits adiscrepancy with observations during high solar activity epochs. For instancein Hermanus, the difference between GPS TEC and NeQuick TEC ( Δ TEC) isgenerally lower than 10 TECu in 2009, and it sometimes reaches 20 TECu in2011 and 2012. It is also noticed that NeQuick 2 is more accurate thanNeQuick 1, with an improvement in TEC estimation more significant for thehigh solar activity epochs. The improvement realised in the latest version ofNeQuick is more than 15 % and sometimes reaches 50 %. Keywords. Ionosphere (mid-latitude ionosphere; modelling and forecasting)

annales geophysicae

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