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

The D-layer of the ionosphere doesn’t respond instantaneously to the incoming solar irradiation, rather, there’s a measurable amount of time delay ( Δ t ) between the incoming solar X-ray flux ( ϕ ( t ) ) during a solar flare and the respective change in the electron density profile ( N e ( t ) ). The Δ t depends on the peak of the incoming X-ray flux ( ϕ 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 Δ t over six suitably chosen latitudes of the mid-latitude regions of both hemispheres and analyse the Δ t – ϕ max profile. To analyse the latitude dependence of the dispersed nature of Δ t – ϕ max profile, we define and compute two parameters, namely, (i) the RMS value of the D-layer response time delay ( Δ t rms ) and (ii) the gradient of the slope ( m ) of the linear fitting on Δ t – l o g 10 ( ϕ max ) profile over each of those chosen latitudes. Further, we compute the latitudinal variation of D-layer response time delay ( Δ lat ( Δ t ) ) for selected pairs of chosen latitudes. To analyse the Δ lat ( Δ t ) – ϕ max profile, we compute a third parameter, namely, the RMS value of latitudinal variation of D-layer response time delay ( Δ lat ( Δ 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 Δ t – ϕ max profile.