Spectral character of VLF sferics propagating inside the Earth‐ionosphere waveguide during two recent solar eclipses

Abstract

Effects of solar eclipses on the propagation characteristics of worldwide VLF sferics from lightning activity require more investigation. An attempt was made on the occasion of two solar eclipses during 22nd July, 2009 and 15th January, 2010 to study the effects of the two eclipses on the propagation characteristics of VLF sferics in the Earth‐ionosphere waveguide. Identical experimental setups were used to study the VLF sferics during the two eclipse events. The spectral character of VLF sferics propagating inside the waveguide is studied at a fixed receiver location (23.75°N, 91.25°E) at six discrete frequencies in between 3 and 20 kHz. During both the eclipse events, it is observed that VLF sferics at all the six discrete frequencies is increased from the mean normal average ambient level. The increment peaks around 10–12 kHz with an overall increment of 6.4 dB with respect to its ambient level. The VLF spectral character of enhancement of sferics show similar characters in two eclipses. The percentage decrease in electron density using standard modeling equations is found to be 90% at the height of 71 km for both the eclipses, supporting linear variation of electron density with solar radiation at the D‐region of the ionosphere. The results are explained qualitatively on the basis of a decrease in electron density at the lower ionosphere modifying the reflection coefficient which affected the propagation of VLF sferics in Earth‐ionosphere waveguide during eclipsed condition.

The 22 July 2009 Total Solar Eclipse: Modeling D Region Ionosphere Using Narrowband VLF Observations

“…In order to get the unique values of H ′ and β with only amplitude data, we have selected most appropriate set of H ′ and β after several iterations of LWPC code, which very closely matched with the observed VLF signal. In order to validate chosen values of H ′ and β from LWPC code for perturbed amplitude, we have used similar method as used by many other workers in absence of good phase data (Guha et al, ; Maurya et al, ; Phanikumar et al, ). The final values of H ′ and β obtained for the VLF variations due to 22 July TSE are presented in Table .…”

“…Since past several decades, TSEs' studies using VLF waves have given episodically chances to study D region ionosphere. There are reports on the D region studies by using VLF observations during several TSEs (e.g., Clilverd et al, 2001;Guha et al, 2010Guha et al, , 2012Kumar et al, 2016;Maurya et al, 2014;Ohya et al, 2012;Phanikumar et al, 2014;Reeve & Rycroft, 1972;Singh et al, 2012Singh et al, , 2011. But still, studies are limited because of the rare occurrence of TSEs.…”

Long‐duration geomagnetic storm effects on the D region of the ionosphere: Some case studies using VLF signal

“…VLF/LF navigational signals studied from our location (23.75°N, 91.25°E) have already been studied during various solar‐terrestrial events like geomagnetic storms, solar eclipse, meteor showers, thunderstorms, etc. [ Sarkar and De , ; De and Sarkar , ; Guha et al ., , , , ].…”

Effect of the total solar eclipse of 20 March 2015 on the ELF propagation over high‐latitude paths

“…Extensive observations of this type were conducted in the VLF band by using the natural tweek atmospherics as well as the signals of VLF broadcasting stations [Crary and Schneible, 1965;Reeve and Rycroft, 1972;Clilverd et al, 2001;De et al, 2011;Singh et al, 2011;Guha et al, 2012;Han and Cummer, 2010]. Similar measurements in the ELF band are as of now absent.…”