Man Hua
Upper Limit of Outer Radiation Belt Electron Acceleration Driven by Whistler‐Mode Chorus Waves
The discovery of the Earth’s radiation belt in 1958 was a major milestone in geophysics and astronomy, which marked the birth of magnetospheric physics. The energetic electrons in the radiation belt, also known as “killer” electrons, pose a huge hazard to Earth-orbiting satellites as well as to our unprecedented space-based connection-dependent society. It is important to understand the underlying physical processes that contribute to the extreme case of the radiation environment. Our study revealed for the first time the natural upper limit of electron acceleration by chorus waves, which provides a new explanation of the observed most intense radiation environment apart from the previous theory that has been accepted for almost 60 years [Hua et al., 2022, GRL, https://doi.org/10.1029/2022GL099618].
[Hua et al., 2022, Geophysical Research Letters]
We test a chain of processes with several potential successive steps that is believed to accelerate the outer bet relativistic electrons to their maximum fluxes during geomagnetic storms. By systematically investigating the correlation between each part of this chain, we intend to identify the critical steps for the relativistic electrons to reach their maximum fluxes. Based on 5-years of Van Allen Probes observations, our results demonstrate that it is the intense and prolonged substorms that produce sustained source and seed electrons, which are strongly associated with the maximum fluxes of relativistic electrons. Furthermore, the increasing correlation between the source electrons and the chorus wave amplitude with increasing levels of substorms supports the significant impact of chorus waves on acceleration of the relativistic electrons during intense substorms. Our results are crucial to advance the current understanding of dominant physical mechanism that controls the outer belt relativistic electron acceleration.
Testing the key processes that accelerate outer radiation belt relativistic electrons during geomagnetic storms
[Hua et al., 2023, Frontiers in Astronomy and Space Sciences]
Very-Low-Frequency transmitters bifurcate energetic electron belt in near-earth space
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.
[Hua et al., 2020, Nature Communications]