Solar flare induced ionospheric D-region perturbation as observed at a low latitude station Agra, India

Abstract

The results of solar flare induced D-region perturbation studies along a short great circle path (GCP=6690 km) lying entirely in the low and equatorial latitude region are presented. We use SoftPAL receiver at Agra (Geograph. lat. 27.2°N, long. 78°E), India and monitor NWC signal (f=19.8 kHz) transmitted from Australia. We analyze the data for the year 2011 and find that the results of amplitude and phase perturbations, time delay, zenith angle independence, and electron density variation in the lower ionosphere are consistent with those observed along similar paths at low and high latitudes. The new work includes; (i) the distribution of peak X-ray flares in the mixed solar cycle period 2011 responsible for clear and measurable sudden phase anomalies (SPAs) is different from that in minimum solar cycle period, though the cut off hardening factor is the same; (ii) the phase anomalies are evaluated in terms of X-ray fluence (J/m2); (iii) the perturbation due to X-class of flare is used to calculate the electron densities in 70–60 km height range which are found to be 60–80 % lower than those in the polar region where X-ray flare is followed by solar proton event.