Fast Acceleration of ``Killer'' Electrons and Energetic Ions by Interplanetary Shock Stimulated ULF Waves in the Inner Magnetosphere

Energetic electrons and ions in the Van Allen radiation belt are the number one space weather threat. How the energetic particles are accelerated in the Van Allen radiation belts is one of major problems in the space physics. Very Low Frequency (VLF) wave-particle interaction has been considered as one of primary electron acceleration mechanisms because electron cyclotron resonances can easily occur in the VLF frequency range. However, recently, by using four Cluster spacecraft observations, we have found that after interplanetary shocks impact on the Earth’s magnetosphere, the acceleration of the energetic electrons in the radiation belt started nearly immediately and lasted for a few hours. The time scale (a few days) for traditional acceleration mechanism of VLF wave-particle interaction, as proposed by Horne et al. [1], to accelerate electrons to relativistic energies is too long to explain the observations. It is further found that interplanetary shocks or solar wind pressure pulses with even small dynamic pressure change can play a non-negligible role in the radiation belt dynamics. Interplanetary shocks interact with and the Earth’s magnetosphere manifests many fundamental important space physics phenomena including energetic particle acceleration. The mechanism of fast acceleration of energetic electrons in the radiation belt response to interplanetary shock impact contains three contributing parts: (1) the initial adiabatic acceleration due to the strong shock-related magnetic field compression; (2) then followed by the drift-resonant acceleration with poloidal ULF waves excited at different L-shells; and (3) particle acceleration due to fast damping electric fields associated with ULF waves. Particles will have a net acceleration since particles in the second half circle will not lose all of the energy gained in the first half cycle. The results reported in this paper cast new lights on understanding the acceleration of energetic particles in the Earth’s Van Allen radiation belt. The results of this study can be widely used in interplanetary shock interacting with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune, and other astrophysical objects with magnetic fields.