Variations in the Maximum Electron Density of the F<sub>2</sub> Layer (NmF<sub>2</sub>) over the Middle Latitude Station of Grahamstown, South Africa, during Solar Cycle 23

Abstract

Ultraviolet (UV) and X-ray radiation are the primary causes of ionization that produce electron density in sufficient quantities to promote the propagation of satellite radio signals in the ionosphere. The electron densities suffer from spatio-temporal variations, and this poses different degrees of threats to satellite radio signals propagating through the ionosphere. We aimed to characterize the maximum electron density of the F<sub>2</sub> layer (N<sub>m</sub>F<sub>2</sub>) in the middle-latitude ionosphere over Grahamstown, South Africa (Geographic latitude: 33.30°S, Geographic longitude: 26.50°E; Geomagnetic Latitude: 33.92°S, Geomagnetic Longitude: 89.37°E). The mean N<sub>m</sub>F<sub>2</sub> data for solar cycle 23 (1998–2008) were used for the studies. The data were grouped into the high solar activity (HSA: 2000–2002), moderate solar activity (MSA: 1998–1999, 2003–2005), and low solar activity (LSA: 2006–2008) years. N<sub>m</sub>F<sub>2</sub> variations were characterized based on the diurnal, seasonal, monthly, and annual data. Also, the correlation between N<sub>m</sub>F<sub>2</sub> and the sunspot number was investigated. Results on diurnal and seasonal variations revealed that noontime bite-out of N<sub>m</sub>F<sub>2</sub> was observed during the June solstice every year. However, it was not observed in the other three seasons. Equinoctial asymmetry is observed to show insignificant annual and solar cycle variations. The seasonal and annual variations of N<sub>m</sub>F<sub>2</sub> with sunspot number were linear (exception: June solstice for MSA, the year 1999; HSA, years 2000–2001). The results reveal that the correlation between N<sub>m</sub>F<sub>2</sub> and the sunspot number was insignificant under conditions of the annual, solar cycle, and latitudinal variations (exception: MSA, the year 2005; negative correlation (0.64)).