Very-Low-Frequency transmitters bifurcate energetic electron belt in near-earth space

Abstract

Very-Low-Frequency (VLF) transmitters operate worldwide mostly at frequencies of 10–30 kilohertz for submarine communications. While it has been of intense scientific interest and practical importance to understand whether VLF transmitters can affect the natural environment of charged energetic particles, for decades there remained little direct observational evidence that revealed the effects of these VLF transmitters in geospace. Here we report a radially bifurcated electron belt formation at energies of tens of kiloelectron volts (keV) at altitudes of ~0.8–1.5 Earth radii on timescales over 10 days. Using Fokker-Planck diffusion simulations, we provide quantitative evidence that VLF transmitter emissions that leak from the Earth-ionosphere waveguide are primarily responsible for bifurcating the energetic electron belt, which typically exhibits a single-peak radial structure in near-Earth space. Since energetic electrons pose a potential danger to satellite operations, our findings demonstrate the feasibility of mitigation of natural particle radiation environment.

Statistical Distribution of Bifurcation of Earth's Inner Energetic Electron Belt at Tens of keV

“…Figure 1h indicates the flux ratio, which is the smaller one of aforementioned ratio1 and ratio2. Overall, the flux ratio is above ∼0.8, which agrees with previous studies that the electron loss due to VLF scattering effects is a relatively slow process (Claudepierre et al, 2020a;Hua et al, 2020;Ross et al, 2019).…”

“…4. The L-shell distribution of the bifurcation dip, energy, and seasonal dependences of the occurrence of bifurcated inner electron belt supports the important role of VLF transmitter signals in electron flux decay in the inner belt in addition to other naturally occurring waves (Hua et al, 2020). The present statistics is therefore crucial to understand when and where the VLF transmitters can efficiently scatter energetic electrons (at tens of keV) in near-Earth space.…”

“…A recent study of Claudepierre et al (2020a) reported bifurcated inner electron belt with a local minimum in the flux radial profile over L = 2-3 from August 2016 to February 2017 based on the raw electron flux measurements from the MagEIS (Blake et al, 2013) onboard Van Allen Probes (Mauk et al, 2013), which is energy dependent and consistent with the location where VLF transmitters can theoretically cause efficient scattering effects (Claudepierre et al, 2020a;Ross et al, 2019). The study of Hua et al (2020) further provided direct quantitative evidence by a case study that VLF transmitters are primarily responsible for bifurcating the energetic electron belt at tens of keV by comparing the results from Van Allen Probes observations and Fokker-Planck diffusion simulations, while other waves including plasmaspheric hiss and lightning-generated whistlers cannot cause bifurcation but can contribute to electron flux decay at higher energies.…”

“…Besides, the pitch angle scattering of electrons at energies of tens of keV due to VLF transmitter waves is most efficient at L > ∼2.2 (Hua et al, 2020). This comparison suggests that the formation of inner belt bifurcation more likely occurs on a relatively flat radial profile of enhanced electron fluxes due to injections or radial diffusion.…”

Prediction of Dynamic Plasmapause Location Using a Neural Network

“…Nowadays artificial neural networks (ANN) (e.g., Hebb, 1949;Marr & Poggio, 1976;McCulloch & Pitts, 1943) are extensively used in the approximation of functions, classification, pattern recognition, and clustering. Neural networks are capable of mapping complicated nonlinear functions between inputs and outputs (Zhelavskaya et al, 2016).…”