Diagnostics of the Solar X-Flare Impact on Lower Ionosphere through the VLF-NAA Signal Recordings

Abstract

An analysis of four solar flare X-ray irradiance effects on VLF signal amplitude and phase delay variations on the NAA/24.0 kHz signal trace during the period from 2005 September to 2006 December was carried out. Solar flare data were taken from the GOES12 satellite one-minute listings. For the VLF data, recordings at the Institute of Physics, Belgrade were used. It was found that solar flare events affect VLF wave propagation in the Earth-ionosphere waveguide lowering the changes of the ionosphere electron density height profiles. This follows from the variation during the solar flare events of the following propagation parameters: the sharpness of the lower edge of the ionosphere and the reflection height.

Sensing the Earth’s low ionosphere during solar flares using VLF signals and goes solar X-ray data

“…Corresponding N e at altitude 74 km for all analyzed characteristic times are given in Table 2. Since the GQD signal amplitude and phase delay perturbations especially in case of C9.7 and M2.5 X-ray flare events (07 April Thomson, 2004;Kolarski et al, 2011;Nina et al, , 2012a.…”

“…Although the effects on VLF signal amplitude and phase delay which are induced by X-ray solar flare events can always be clearly noticed and recognized, the flare events with the same characteristics (class, duration, zenith angle of incidence radiation) can cause different types of amplitude and phase delay perturbations depending on which VLF signal trace it is monitored. For example, all four flare events which have been analyzed in this paper on GQD signal, in case of NAA/24.0 kHz signal (the GCP distance 6540 km) are characterized with "mirror" type of VLF signal reflection at the Belgrade receiver site (Kolarski et al, 2011). "Mirror" type of signal reflection is characteristic for NAA signal received at the Belgrade receiver site regardless of the flare event strength (Kolarski et al, 2011).…”

Behaviour of electron content in the ionospheric D-region during solar X-ray flares

“…Modeling the signal propagation requires knowledge of electron density dependence on space and time. In this paper, the electron density during an X-ray flare is determined by a procedure given in Grubor et al (2008) and used in many other papers (see for exampleŽigman , Kolarski et al 2011, Nina et al 2011, 2012a. This procedure is based on matching the observed VLF signal data, the amplitude ∆A rec and phase ∆P rec changes, with corresponding results of simulations ∆A sim and ∆P sim of the VLF signal propagation using the Long-Wave Propagation Capability (LWPC) numerical model developed by the Naval Ocean Systems Center (NOSC), San Diego, USA (Ferguson 1998).…”

“…The research in this field includes scientific analyses of various phenomena in the ionosphere such as e.g. lightnings (Inan et al 2010), tectonic motions (Astafyeva andAfraimovich 2006, Dautermann et al 2009), the sunrise and sunset (Afraimovich et al 2009, Nina andČadež 2013, solar eclipses (Singh et al 2011, Maurya et al 2014, Verhulst et al 2016, γ ray burst (Inan et al 2007, Nina et al 2015a, solar activity (Kolarski et al 2011, Nina et al 2011, 2012a,b, Schmitter 2013, Sulić and Srećković 2014, Satori et al 2016, nuclear explosions (Madden and Thompson 1965, Yang et al 2012, Zhang and Tang 2015 as well as ionospheric harmonic and quasi-harmonic hydrodynamic motions (Jilani et al 2013, Nina andČadež 2013. However, the ionosphere has also a very important role in practical applications, primarily in telecommunications (Bajčetic et al 2015, Alizadeh et al 2015.…”

Responses of the ionospheric D-region to periodic and transient variations of the ionizing solar Lyα radiation

“…In this paper, we present different kinds of variation in the lower ionospheric plasma that are induced by changes in Lyα ionization resulting from different astrophysical phenomena such as Earth's rotation and revolution, variations of sunspot number during solar cycle, solar eclipses and solar flares. For monitoring the lower ionosphere we use a method based on very low frequency (VLF) radio waves propagation, as used in numerous published studies (Clilverd, Thomson, & Rodger, 1999;Ilić et al, 2017;Inan, Cummer, & Marshall, 2010;Nina, Čadež, Šulić, Srećković, & Žigman, 2012;Kolarski, Grubor, & Šulić, 2011;Kolarski & Grubor, 2014;Nina & Čadež, 2014;A. K. Singh, A. K. Singh, R. Singh, & R. P. Singh, 2014;Šulić & Srećković, 2014;Šulić, Srećković, & Mihajlov, 2016;Bajčetić, Nina, Čadež, & Todorović, 2015).…”