Quantitative Modeling of Lower Ionospheric Response Due to Solar X-ray Flare: A Propagating Radio Wave Simulation Approach

Abstract

The ionosphere is an expansive natural detector and it characteristically reacts to ionizing influences coming from sun and other extraterrestrial energetic sources. In this article, first we give a brief review of earlier works performed specifically on Very Low Frequency (VLF) radio signal interaction with D-region ionosphere. Those are mainly related to the D-region ‘response time delay’ as experienced by VLF signal (△ t), effective recombination coefficient (αeff) and its connection with the D-region electron density (Ne) and other essential parameters during X-ray solar flares. Further, we present the measurement techniques and the observed results regarding the same time delay (△ t) experienced by VLF signal with respect to the X-ray flux variation of solar flares. Several research groups have developed many lower ionospheric models based on theoretical and experimental results to deal with those above mentioned quantities. We follow a rather simplified model proposed by J. Wait for D-region through the Long Wave Propagation Capability (LWPC) numerical code to estimate the Ne using flare induced amplitude-perturbation (△ A). Now, we use this △ t and Ne-profile for estimation of the effective recombination coefficient (αeff). Lastly, we analyse the results and conclude.