Validation of IRI-2007 ionospheric model predictions over the Tehran area during a low solar activity period

The outer part of the upper atmosphere, the ionosphere, is where free electrons formed by solar X-rays and extreme ultraviolet (EUV) radiation play an important role in radio and satellite communication. Knowledge of the critical frequency and maximum electron density of the F2 ionospheric layer distribution is crucial for ionospheric storm studies and the estimation and correction of propagation delays in telecommunications. It has proven that the F2 ionospheric layer can significantly affect the propagation of radiowaves. The ionosphere can be used to reflect radio signals over long distances. Indeed,the ionosphere is an efficient reflector with frequencies below approximately 30 MHz.Also, it can be useful to study the variability of the F2 ionospheric layer to show that thislayer is affected primarily by space weather phenomena, mostly of solar origin such as thesolar zenith angle, solar ionizing radiation, and the solar cycle. These extraterrestrialphenomena control the ionosphere from above. Some other waves enter the ionospherefrom below and can cause some significant changes in the F2 ionospheric layer.The International Reference Ionosphere (IRI) model is a standard model of the ionosphere supported by the Committee on Space Research (COSPAR) and InternationalUnion of Radio Science (URSI). The IRI model has many practical applications in HighFrequency (HF) predictions. The IRI model offers a description of the average ionosphere. It is a mathematical description of the ionosphere as a function of location,time, altitude, solar activity and geomagnetic activity. Periodic updates to this model areessential to maintaining its prediction ability. A large number of independent studies haveevaluated the IRI model in comparisons with direct and indirect ionospheric measurements, those not used in the model development. A favorable comparison withIRI model is often one of the major goals of ionospheric teams all over the world.In this work, to evaluate the latest available ionospheric model, IRI-2007, we haveobtained hourly monthly values of foF2 and NmF2 over the Tehran area (35.4N,51.2E,52.7dip) during low solar activity period, in which the Rz12 (12-month running averagesunspot number) varies between 7.7 and 15.3 from July 2006 to June 2007. Datameasured using the IPS-71 at the ionospheric station at the Institute of Geophysics at theUniversity of Tehran (35.4N, 51.2E, 52.7dip) were used to perform the calculations.Subsequently, the observed critical frequency and maximum electron density of the F2ionospheric layer is compared with IRI-2007 model predictions. To run the IRI2007model, the URSI and CCIR coefficients were used.Our study shows that values of the foF2 and NmF2 parameters have the highest valuesduring the daytime hours and the lowest values occur at pre-sunrise hours. Our studyshows that the IRI-2007’s ability to predict semi-annual anomalies with a maximumelectron density of the F2 ionospheric layer are most accurate in the summer and less soduring the autumn and spring.In general, the predictions obtained with CCIR and URSI are similar. Our results showthat IRI-2007 can successfully predict the critical frequency and maximum electrondensity of the F2 ionospheric layer. Additionally, our study shows that differencesbetween the foF2(OBS) and the foF2(IRI-2007) remains below 12% during all seasons.The best agreement occurs during the summer and winter, and the largest differences are observed in the spring and autumn. The average percentage deviation of a full yearregisters at approximately 6.5% for CCIR and nearly 8% for URSI coeffecients.Moreover, our results show that the percentage deviation between the NmF2(OBS) andthe NmF2(IRI-2007) remains lower than 21% during all seasons. The total averagepercentage deviation of a full year is approximately 13% for the CCIR coefficient andnearly 16.5% for the URSI.