foF2 variability at a southern low-latitude station and the performance of IRI-2016 model during ascending phase of solar cycle-24

In this research, we have analyzed the data of the critical frequency of the F-2 region (foF(2)) ionosphere over the southern low-latitude station COCO (Keeling) Island (Geog. Lat. 12.20 degrees S; Geomag. Lat. 22.83 degrees S; Geog. Long. 96.80 degrees E) for the period 2009-2013 and thereof have compared the results with those obtained with the IRI-2016 model. Our analysis shows a good correlation between variations in foF(2) and solar flux at an F10.7 cm wavelength. With regard to geomagnetic activity during 2009-2013, it has been found that the variability in the monthly mean Ap index remained below 20 nT throughout the period 2009-2013. Concerning quiet time F2 region variability, our results explicated solar cycle, semiannual, and seasonal/annual variations in foF(2). Similar oscillations in foF(2) have been explored using the Lomb-Scargle periodogram technique. We have also observed the fundamental mode (27 days) and its overtones (9- and 13-day) in the geomagnetic activity parameter (Ap). Analysis of foF(2) showed the consistent presence of the semiannual anomaly and absence of the winter anomaly during the ascending phase of solar cycle-24. The presence of an annual component in normalized foF(2) has been examined using regression analysis. A comparative study of ionosonde-observed foF(2) with IRI-2016-modeled foF(2) showed that the general ionospheric trends in IRI predictions are consistent with the observations for the diurnal, seasonal, and solar cycle variations. However, a deviation in the amplitude of foF(2)up to the order of 5 MHz depending on local time, seasons, and phases of the solar cycle, respectively, has been observed. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.