Comparison of peak characteristics of the F_2 ionospheric layer obtained from the Cyprus Digisonde and IRI-2012 model during low and high solar activity period

摘要

We investigate first the climatology expressed by diurnal and seasonal variations of the critical frequency (f_oF_2) and the peak height (h_mF_2) of the F_2-layer derived from digital ionosonde measurements at the low-middle latitude European station in Nicosia, Cyprus (geographical coordinates: 35°N, 33°E, geomagnetic lat. 29.38°N, I=51.7°). Monthly median hourly values of the F_2-layer peak characteristics are obtained using manually scaled data during the 5-year period 2009-2013. The observational results are then compared with the International Reference Ionospheric Model (IRI-2012) predictions using both URSI and CCIR coefficients. It is shown that the semi-annual pattern of daytime f_oF_2 characterized by higher values at equinoxes than either solstices as well as the winter anomaly phenomenon demonstrate strong solar activity dependence. An annual pattern of night-time f_oF_2 is also detected with lower values in winter and higher in summer. The seasonal variation of daytime h_mF_2 is evident and peaks of h_mF_2 at pre-sunrise and post-sunset hours are identified during December. The IRI-2012 model is capable to capture the main diurnal and seasonal patterns of f_oF_2 and h_mF_2. The highest overestimation of daytime f_oF_2 is noted at equinoxes and solstices except from March, October, December of 2011, and June of 2013. Significant f_oF_2 underestimation is observed at evening and after midnight during February and March of 2009. Large positive discrepancies between the modeled and observed h_mF_2 values are noticed during the deep solar minimum year 2009. Overall, IRI-model estimates are more accurate for h_mF_2 than f_oF_2 over Cyprus and for the examined period.