Investigation of Daytime Electromagnetic Power in the Topside Ionosphere Radiated From VLF Transmitters During Solar Minimum Period of Cycle 23/24

Abstract

The propagation of Very Low Frequency (VLF) waves from ground-based VLF transmitters worldwide allows them to penetrate the ionosphere and enter the magnetosphere. This interaction drives electron precipitation in the inner radiation belts through resonant interactions. The energy loss of VLF waves penetrating the ionosphere occurs mainly in the lower ionosphere, which is mainly affected by solar shortwave radiation. However, the solar activity affecting the energy of VLF transmitter signals reaching the topside ionosphere has not been sufficiently studied during the solar minimum period. In this paper, we quantify the correlation between the electromagnetic field radiated to the topside ionosphere by different VLF transmitters and solar activity, as well as the energy injected into the topside ionosphere during the daytime, using data from the DEMETER satellite. Our findings demonstrate that both the average daytime radiated electric field and magnetic field above the four VLF transmitters are negatively correlated with solar activity. Furthermore, even during the lower solar activity years, the radiated power in the topside ionosphere from VLF transmitters in the winter of 2008 during the daytime was found to be more than 2.5 times higher than that in the winter of 2004.