English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

. The signals from VLF/LF transmitters are known to propagate in the Earth-ionosphere waveguide, so that the subionospheric propagation characteristics are very sensitive to the condition of the lower ionosphere. We know that there appear the terminator times just around the sunrise and sunset in the diurnal variation of subionospheric VLF/LF signal (amplitude and phase). These terminator times are found to shift significantly just around an earthquake, which enables us to infer the change in the ionosphere during the earthquake. In this paper we try to understand the physical mechanism on the generation of those terminator times for relatively short propagation path (less than 2000 km) by means of wave-hop method. It is found that the lowering of the ionosphere boundary during an earthquake decreases the path length of the sky wave and this alters the interference condition of this wave with the ground wave, which lead to an appearance of terminator times as the destructive interference between the ground and sky waves. Finally, we suggest a possible use of terminator time shifts to investigate the lower ionospheric plasma changes during the earthquakes.

On the generation mechanism of terminator times in subionospheric VLF/LF propagation and its possible application to seismogenic effects