Validation of the IRI 2016, IRI-Plas 2017 and NeQuick 2 models over the West Pacific regions using the SSN and F10.7 solar indices as proxy

Abstract

This paper investigates the validation of the performance of the latest versions of the International Reference Ionosphere (IRI 2016), the IRI extended to the plasmasphere (IRI-Plas 2017) and NeQuick 2 models in the estimation of the variation of the Total Electron Content (TEC) over the West Pacific regions during the 2015–2017 years. This has been performed employing the GPS-derived TEC data obtained from stations located at Observation Rock, OBSR (geog 46.90°N, 238.18°W, Geom. 52.46°N), Husband, HUSB (44.12°N, 238.15°W, Geom. 49.73°N). It has been revealed that both the GPS-derived VTEC and modelled (IRI 2016, IRI-Plas 2017 and NeQuick 2 VTEC) variations attain their minima at about 13:00 UT (05:00 LT) and maxima at about 20:00 UT (12:00 LT). Moreover, because of the enhancement of photo-ionization process in the region as a result of exposure of the ionosphere for direct radiation in the summer months, large measured VTEC values are seen in the June solstice months during 2015–2017. It has also been shown that, because of the variation of the Sunspot number (SSN) and solar radio flux 10.7 cm (F10.7), the VTEC variations for both the GPS-derived and models show decrease at transition from 2015 to 2017, with some exceptions observed in the June solstice months. In addition, the root-mean-square deviations (RMSD) between the GPS-derived and modelled diurnal VTEC variations are generally less than 0.5TECU in using both the SSN and F10.7 indices. This shows that all the three models are good in TEC estimation with the IRI-Plas 2017 and NeQuick 2 perform the best on most of the hours, in comparison with the IRI 2016 model with IRI2001 option, especially in using the F10.7 index when the solar activity increases. However, when the solar activity decreases, utilizing the SSN for all the three models (especially for the IRI-Plas 2017 and NeQuick 2) shows the better performance. Moreover, during the geomagnetic storm condition, both the IRI 2016 and IRI-Plas 2017 models with the storm option “on” do not adequately reflect to the sharp increase or decrease of the GPS-derived VTEC values.