Propagation characteristics of VLF signal and lightning sferics within equatorial Earth-ionosphere waveguide during two solar eclipses

Abstract

Two long duration solar eclipses having totality over Earth's equatorial region, within a period of six months is a rare event. The results from such two solar eclipses, one on 22nd July, 2009 and another on 15th January, 2010, on VLF propagation is presented in this paper. From the amplitude variation of a transmitted VLF navigational signal at 18.2 kHz (VTX3, 8.38° N, 77.75° E) over a Great Circle Path (GCP) of 2200 km, the virtual reflection height H′ and inverse scale height parameter (β) of the eclipsed lower ionosphere are estimated. Modeling shows that during maximum eclipse over the path, an average 80% drop in electron density occurs at a height of 71 km at the equatorial lower ionosphere. At the same time, the intensity of sferics from lightning at different frequencies is found to increase during both the eclipses. The spectral variations of sferics increment in both the eclipses are almost identical having a correlation coefficient of 0.88 with a statistical significance of 98%. The results are explained on the basis of decrease in electron density at the lower ionosphere, modifying the reflection coefficient which affected the propagation of VLF sferics in Earth-ionosphere waveguide under eclipsed condition.