Global Ionospheric Response to X-Class Flares During the Solar Cycle 24: An Investigation Using IGS Network

Abstract

In this study, we have comprehensively investigated the ionospheric response to all the 49 X-class flares that occurred during the solar cycle 24, using high-cadence Total Electron Content (TEC) measurements obtained from International Global Navigation Satellite System Service (IGS) networks, spanning more than 500 stations across the globe. GOES measured X-ray emissions in the 0.1–0.8 nm band and SOHO-recorded extreme ultraviolet (EUV) radiations in the 26–34 nm band have been used to characterize the flare radiations. The analysis of spatial variability in global distribution of flare-induced TEC ($\Delta$TEC) indicates a clear-cut dependence on Solar Zenith Angle (SZA). The ratio of $\Delta$TEC at $\text{SZA}=90°$ to that at $\text{SZA}=0°$ was found to vary from 0.13 to 0.87, with an average value of 0.45. The non-linear increase in X-ray and EUV during the flares has been corrected by incorporating the Central Meridian Distance (CMD) on X-ray measurements and found that the correlation between $\Delta$TEC and $\Delta$X-ray has been increased from 0.45 to 0.93. The CMD effect was more pronounced for stronger flare classes and those occurring closer to the solar limb. The inter-comparison of these results with the previous cycle indicates that overall features match fairly well despite the reduced activity and fewer flares in cycle 24. The importance of the study lies not only in showing the quantitative analysis of global flare-induced ionospheric variability during solar cycle 24, probably for the first time, but also helpful for “space weather” predictions in view of its relevance in communication and navigation scenarios.