Response of the equatorial lower ionosphere to the total solar eclipse of 22 July 2009 during sunrise transition period studied using VLF signal

摘要

Changes in equatorial D-region electron density are studied using subionospherically propagating VLF signal at 18.2 kHz over a distance of 2200 km during the total solar eclipse of 22 July 2009. There are very few studies about the eclipse's effects on the equatorial lower ionosphere in the scientific literature. In the light of that, the objective of the present work is to study the effects of the eclipse on the dynamics of the equatorial lower ionosphere during ionospheric sunrise transition period. In the present case, great circle path between VLF transmitter and receiver falls totally in partial eclipse zone, having a maximum solar obscuration of 90 and an average obscuration of 74. Results show an average decrease of 3.2 dB in signal strength compared to control days during peak solar obscuration over the path. A comparison with previous studies shows an increase both in lower ionosphere virtual reflection height (H') and Wait inverse scale height parameter (β); the values estimated are 74.5 km and 0.46 km~(-1) compared to unperturbed ionosphere values of 71 km and 0.43 km~(-1), respectively. During maximum eclipse over the path, the model profile shows an average 80 drop in electron density at a height of 71 km at equatorial lower ionosphere. A nonlinear variation of lower ionosphere electron density with solar radiation is found as opposed to the model study proposed by previous workers.