Quantitative analysis of lower ionospheric response time delay associated to the solar flares

Abstract

The D-layer of the ionosphere doesn’t respond instantaneously to the incoming solar irradiation, rather, there’s a measurable amount of time delay ($\Delta t$) between the incoming solar X-ray flux ($\phi (t)$) during a solar flare and the respective change in the electron density profile ($N_e(t)$). The $\Delta t$ depends on the peak of the incoming X-ray flux ($\phi _{max}$) during the flare. We solve the ‘electron continuity equation’ for the D-layer by numerical method for a selected set of 455 solar flares to obtain $\Delta t$ over six suitably chosen latitudes of the mid-latitude regions of both hemispheres and analyse the $\Delta t$–$\phi _{max}$ profile. To analyse the latitude dependence of the dispersed nature of $\Delta t$–$\phi _{max}$ profile, we define and compute two parameters, namely, (i) the RMS value of the D-layer response time delay ($\Delta t_{rms}$) and (ii) the gradient of the slope (m) of the linear fitting on $\Delta t$–$log_{10}(\phi _{max})$ profile over each of those chosen latitudes. Further, we compute the latitudinal variation of D-layer response time delay ($\Delta _{lat}(\Delta t)$) for selected pairs of chosen latitudes. To analyse the $\Delta _{lat}(\Delta t)$–$\phi _{max}$ profile, we compute a third parameter, namely, the RMS value of latitudinal variation of D-layer response time delay ($\Delta _{lat}(\Delta t)_{rms}$). We do a comparative analysis of these parameters across the chosen set of latitudes. Finally, we conclude quantitatively with possible explanations about the systematic latitude dependence and variation of the dispersed nature of $\Delta t$–$\phi _{max}$ profile.