Preprints
https://doi.org/10.5194/angeo-2023-38
https://doi.org/10.5194/angeo-2023-38
11 Jan 2024
 | 11 Jan 2024
Status: this preprint is currently under review for the journal ANGEO.

Investigation of the October effect in VLF signals

Marc Hansen, Daniela Banyś, Mark Clilverd, David Wenzel, and M. Mainul Hoque

Abstract. Subionospheric Very Low Frequency (VLF) radio signals are reflected by free electrons in the ionospheric D-region at about 60–90 km altitude and can propagate over long distances, which makes them useful for monitoring the state of the D-region or perturbations due to solar flares. At the D-region height, the ionosphere is mainly ionized by the solar Lyman-α radiation. The reflection characteristics of VLF signals depend on the state and dynamics of the D-region which is highly influenced by the Lyman-α radiation. Although the amplitude of the received terrestrial VLF signal changes as a function of solar zenith angle over the course of the year, the VLF amplitude shows a distinctive sharp decrease around October, which is hence called the “October effect”. This study investigates the occurrence of the October effect and its dependencies on latitude and longitude. We developed a method to detect the occurrence of the October effect in the long-term VLF data and derive key parameters characterizing (start and end date, intensity) the sudden decrease in the signal amplitude. This investigation using a network of VLF stations distributed over low, middle and high latitude regions shows that the occurrence of the October effect has a clear latitudinal dependency, occurring earlier in high-latitude regions than at mid-latitudes. No low latitude signature is found.

Marc Hansen, Daniela Banyś, Mark Clilverd, David Wenzel, and M. Mainul Hoque

Status: open (until 05 Apr 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on angeo-2023-38', Anonymous Referee #1, 01 Feb 2024 reply
Marc Hansen, Daniela Banyś, Mark Clilverd, David Wenzel, and M. Mainul Hoque
Marc Hansen, Daniela Banyś, Mark Clilverd, David Wenzel, and M. Mainul Hoque

Viewed

Total article views: 269 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
229 32 8 269 7 7
  • HTML: 229
  • PDF: 32
  • XML: 8
  • Total: 269
  • BibTeX: 7
  • EndNote: 7
Views and downloads (calculated since 11 Jan 2024)
Cumulative views and downloads (calculated since 11 Jan 2024)

Viewed (geographical distribution)

Total article views: 269 (including HTML, PDF, and XML) Thereof 269 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 02 Mar 2024
Download
Short summary
The VLF amplitude does not show a symmetrical behavior over the year, which would be expected from its dependency on the solar position. The VLF amplitude rather shows a distinctive sharp decrease around October, which is hence called the “October effect”. This study is the first to systematically investigate this October effect, which shows a clear latitudinal dependency.