Long‐Term Variations of Energetic Electrons Scattered by Signals From the North West Cape Transmitter

• Published in: Space weather Vol. 22; no. 3
• Main Authors: Hu, Jingle, Xiang, Zheng, Ma, Xin, Liu, Yangxizi, Dong, Junhu, Guo, Deyu, Ni, Binbin
• Format: Journal Article
• Language: English
• Published: 01.03.2024
• ISSN: 1542-7390; 1542-7390
• DOI: 10.1029/2023SW003827

Very‐low‐frequency (VLF) signals emitted from ground‐based transmitters for submarine communication can penetrate the ionosphere and leak into the magnetosphere, leading to electron precipitation via wave‐particle interaction and thereby providing a potential means for radiation belt remediation. In this study, we systematically analyze the dependence of quasi‐trapped electron fluxes scattered by signals from the North West Cape (NWC) transmitter on electron energy, L‐shell, and geomagnetic activity (i.e., the Dst index) using long‐term measurements from the DEMETER satellite. Considering potentially changed theoretical cyclotron resonant condition, we find that the variations of wave normal angle (WNA) of NWC transmitter signals or of the background electron density can explain the variated “wisp” positions in energy versus L plane. The long‐term data analyzation suggests that the energy‐dependences increases can help to distinguish the different source mechanisms of quasi‐trapped electrons. The enhancement of quasi‐trapped electron fluxes induced by NWC transmitter signals is more obvious at L = 1.8 than L = 1.6 due to higher trapped flux levels and strong pitch angle diffusion induced by transmitter signals. Plain Language Summary There are a number of man‐made powerful very‐low‐frequency (VLF) transmitter stations around the world to support communications of submarines due to relatively large skin depth in sea water. These VLF transmitter signals propagate within the Earth‐ionosphere waveguide and are sensitive to ionospheric and ground properties. When the electron densities in the ionosphere are weak, some VLF transmitter signals can leak into the magnetosphere and interact with energetic electrons in the near‐Earth space. One direct observational evidence of interactions between VLF transmitter signals and energetic electrons is electron flux enhancements observed by Low‐Earth‐Orbit satellites at east of the north west cape (NWC) transmitter. In this study, we investigate the long‐term variations of energetic electrons scattered by NWC transmitter signals using 6‐year observations from the DEMETER satellite. These results provide valuable information regarding the quantitative electron scattering effect of NWC transmitter signals and advance our understanding of radiation belt remediation in terms of wave‐particle interactions. Key Points Enhanced quasi‐trapped electron fluxes induced by North West Cape (NWC) transmitter signals at different energies and L values are explored The variations of wave normal angle of NWC transmitter signals or of background electron density can explain changes of “wisp” position The energy dependence of quasi‐trapped electron fluxes can help to analyze the underlying source mechanisms