Investigation of the Ionospheric Response over Iran to Solar and Geomagnetic Indices Using the SAMI2 Numerical Model

In this study, the effects of the solar radiation index F10.7 and the geomagnetic index Ap on ionospheric characteristics were examined using two-dimensional SAMI modeling, with a focus on the critical frequency foF2, the peak electron density height hmax, and the electron density distribution. In this analysis, F10.7 values of 40, 100, 200, 300, and 400 were investigated for two different days of the year—Day 15 (January 15, winter) and Day 196 (July 15, summer)—and at two times of day, morning (09:00) and afternoon (15:30), with a fixed geomagnetic index of Ap = 100 at a longitude of 60° and latitude of 36°. These two days and two times intervals were selected to compare the effects of solar radiation and geomagnetic activity under varying seasonal and diurnal conditions; Day 15 represents winter conditions, while Day 196 corresponds to summer, allowing observation of the ionosphere’s differing responses to solar radiation.
The results indicate that foF2 increases approximately linearly and positively with increasing solar radiation, whereas hmax exhibits a nonlinear, exponential response, showing particularly significant growth during afternoon hours and at high levels of radiation. Furthermore, hmax was found to be more sensitive to time of day and season than foF2.
In the SAMI2 modeling section, the combined effects of geomagnetic index Ap (100, 200, and 400) and solar radiation F10.7 (100 and 200) on electron density distribution were examined for two days of the year—Day 196 (summer) and Day 349 (winter)—at a longitude of 51°. Day 196 represents summer conditions, and Day 349 represents winter. Selecting these two days enabled comparison of ionospheric behavior under different levels of solar input energy and plasma dynamics.
The results show that increasing Ap produces two differential density peaks near the equator and minima at mid-latitudes, while increasing F10.7 not only enhances the baseline density but also amplifies the magnitude of Ap-induced variations. Comparison of the two days revealed that Day 349 exhibits a stronger response to geomagnetic disturbances than Day 196, demonstrating the dependence of ionospheric structure on temporal conditions and the combined influence of solar radiation and geomagnetic activity.
These findings highlight the importance of accurate and comprehensive ionospheric modeling that accounts for the effects of solar radiation and geomagnetic activity, and they can be applied to improve communication systems, navigation, and space weather monitoring. Moreover, this research represents the first detailed simulation-based investigation of the ionospheric response over Iran under combined geomagnetic and solar-radiation conditions, addressing a critical regional gap in space-weather studies. Understanding these dynamics is essential for countries located in low- and mid-latitude zones, where ionospheric variability strongly affects HF communication, GNSS performance, and technological infrastructure. The results therefore offer valuable insights for enhancing national space-weather forecasting capabilities and strengthening the resilience of communication and navigation systems.