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In this work we study the effect of solar flares on the ionosphere over Cyprus. Solar flares are impulsive solar activity
events usually coupled with Coronal Mass Ejection (CME). The arrival and the subsequent impact of solar flares on
geospace, following an eruption on the Sun’s surface is almost immediate (around 9 min) whereas the impact of CMEs is
rather delayed (2-3 days) as the former is based on X-ray radiation whereas the latter phenomenon is related with
particles and magnetic fields travelling at lower speeds via the Solar Wind. The penetration of X-rays down to the Dregion
following such an event enhances the electron density. This increase can be monitored by ionosondes, which
measure the electron density up to the maximum electron density NmF2. The significance of this increase lies on the
increase of signal absorption causing limited window of operating frequencies for HF communications. In this study the
effect of enhanced X-ray flux on the ionosphere over Cyprus during solar flares has been investigated. To establish the
correlation and extent of impact on different layers, data of X-ray intensity from Geostationary Operational
Environmental Satellite (GOES) and ionospheric characteristics (D & F layer) over Nicosia station (35° N, 33° E) were
examined for all solar flares during the period 2011-2014. The analysis revealed a positive and good correlation between
frequency of minimum reflection, fmin and X-ray intensity for D layer demonstrating that X-rays play a dominant role in
the ionization of lower ionosphere. Hence, X-ray flux can be used as a good proxy for studying the solar flare effects on
lower ionosphere. The correlation coefficient between maximum electron density of F layer, NmF2 and X-ray intensity
was found to be poor.
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