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We present the modeling and analysis of the D-region ionosphere from multiple aspects. Firstly, the study of
sub-ionospheric Very Low Frequency (VLF) signals is notably sensitive to the characteristic changes of
properties which occur in D-region under ambient conditions, as well as, during the solar flares. The soft
solar X-ray perturbs the D-region especially during solar flares. Such solar energetic events can be
investigated remotely by systematic monitoring and analysis of VLF signals. We numerically model the VLF
signature of the effects of solar flares of all possible classes on D-region. We also present some results
regarding the response time delay in D-region during a number of C, M and X classes of solar flares as
obtained from simulations done on the basis of VLF observations. Secondly, we present an alternative aspect
of analysing D-region by numerically solving the ‘electron continuity equation’ and obtaining the electron
density and response time delay profiles during similar classes of solar flares. Two methods are
complementary to each other and together they provide a justified picture of D-region behaviour. |