Publication date: 15 November 2019
Source: Advances in Space Research, Volume 64, Issue 10
Author(s): O.S. Oyekola
Abstract
We have investigated the performance of 2016 International Reference Ionosphere (IRI) at equatorial Ouagadougou (12.4°N, 358.5°E; dip latitude: 1.5°N), Burkina Faso station, using 4 years 5 months of hourly monthly median M(3000)F2 values from January to May 1986 and from January 1987 to December 1990 using Shimazaki (1955) analysis technique. The deduced values of hmF2 are compared with the predictions of the three global IRI-2016 hmF2 model options for four different levels of solar activity with yearly averaged solar flux intensity F10.7 value of 85, 140, 214 and 190, corresponding to a year of 1987 solar minimum, 1988 moderate solar activity, 1989 very high solar activity and 1990 solar maximum, respectively. We find that the three IRI-hmF2 models: SHU-2015, AMTB-2013, and BSE-1979 reproduce the diurnal features of ionosonde-based hmF2 fairly well, showing daytime maximum and the prominent evening peak, except for solar cycle minimum where such feature is absent in Bilitza et al. (1979) and weakly expressed in Shubin (2015) hmF2 models. The magnitudes of the evening peaks in hmF2 for both data and models essentially correlate with solar activity but the occurrence times are independent of the phases of the solar cycle for all models. On average, the dayside maximum occurs between about noon and 1400 LT for both ionosonde-derived hmF2 and IRI models with typical values of 430 and 420 km, while the prominent evening peak in hmF2 occurs between about 1800–1900 LT with characteristic values of 390–450 km. We observed SHU-2015 persistently occur at about 1800 LT with a lower magnitude compared to ionosonde-based hmF2, the digisonde-based hmF2 model (AMTB), and Bilitza et al. (1979) model. We also show that SHU-2015 is consistently and significantly lower in values that the ionosonde hmF2, AMTB-2013 and BSE-1979 models. SHU-2015 deviates from data by about 2 times during low and median solar activity years but diverges by about 3–4 times during very and high solar maximum. Quantitative analyses indicate that the average absolute discrepancy between ionosonde-derived hmF2 and IRI model is 15%, 5.2% and 5.8% for SHU-2015, AMTB-2013, and BSE-1979, respectively. SHU-2015 model root-mean-squared error (RMSE) varies strongly with increasing solar activity with magnitudes roughly within the range ∼41–74 km, whereas AMBT-2013 and BSE-1979 RMSE vary between ∼19–36 km and ∼25–27 km, correspondingly. BSE-1979 RMSE does not exhibit any dependence on solar activity, while AMBT-2013 RMSE appears to decrease with an increase in solar activity. In contrast, SHU-2015 mean-relative-deviation (MRD) increases dramatically with increasing solar activity with values between ∼10–16%. AMTB-2013 and BSE-1979 both indicate a slight decrease with increasing solar activity, with values ranging between ∼3.3–8.9% and ∼4.8–6.7%, respectively. On the basis of evidence provided in this work, we conclude that AMTB-2013 and BSE-1979 have higher accuracy than SHU-2015. Although the hmF2 calculated from ionograms and from empirical formula of Shimazaki could differ rather substantially from the real hmF2 values, especially in the equatorial region. The results of this study show that the AMTB-2013 and BSE-1979 models describes better the hmF2 obtained from the M(3000)F2 values, consequently, we recommend AMTB-2013 and BSE-1979 for equatorial region over West African longitude sector.
