Temporal and Spatial Variation of The Virtual Height of Ionosperic F2–layer Over Two Equatorial Stations During the Minimum to Ascending Phase of Solar Cycle 25

Abstract

The research examines ionospheric F2-layer virtual height (h’F2) variations at Ilorin (14.80°N, 17.40°W) in the Africa sector and Boa Vista (2.80°N, 299.30°E) in the America sector, during Solar Cycle 25's minimum and ascending phases. The aim is to investigate the temporal and spatial variations of the virtual height of the F2-layer over two equatorial stations during the minimum to ascending phase of Solar Cycle 25 at two equatorial stations in two different longitudinal sectors. Analyzing data from these stations statistically, the paper investigates diurnal, seasonal, and annual variations in h’F2.Diurnally, the h’F2 demonstrates greater responsiveness during daytime (06:00 – 18:00 LT) compared to nighttime (18:00 – 05:00 LT). Seasonally, peak values occur around noon and post-noon periods, displaying significant disparities during equinoxes and solstices over both stations in the different solar phases. During the minimum phase year (2020), peak heights of h’F2 reached 387 km at Ilorin and 372 km at Boa Vista. In the ascending phase year (2021), these peaks slightly shifted to 389 km at Ilorin and 404 km at Boa Vista. Annually, the highest peak values of h’F2 occur at noon, measuring 376 km at Ilorin and 331 km at Boa Vista during the minimum phase, while during the ascending phase, both stations recorded almost identical values of 305 km at noon. Overall, h’F2 variation exhibited higher magnitude at Ilorin in the African longitudinal sector than at Boa Vista in the American longitudinal sector during the minimum phase of solar cycle 25, with the reverse observed during the ascending phase. This detailed analysis illuminates the complex variations in ionospheric behavior across various time frames and geographic locations, showcasing substantial variability and sensitivity to solar influences in equatorial stations across Africa and America.