Intense low-frequency chorus waves observed by Van Allen Probes: Fine structures and potential effect on radiation belt electrons

Frequency distribution is a vital factor in determining the contribution of whistler-mode chorus to radiation belt electron dynamics. Chorus is usually considered to occur in the frequency range 0.1\textendash0.8 inline image (with the equatorial electron gyrofrequency inline image). We here report an event of intense low-frequency chorus with nearly half of wave power distributed below 0.1 inline image observed by Van Allen Probe A on 27 August 2014. This emission propagated quasi-parallel to the magnetic field and exhibited hiss-like signatures most of the time. The low-frequency chorus can produce the rapid loss of low-energy (\~0.1 MeV) electrons, different from the normal chorus. For high-energy (>=0.5 MeV) electrons, the low-frequency chorus can yield comparable momentum diffusion to that of the normal chorus, but much stronger (up to 2 orders of magnitude) pitch-angle diffusion near the loss cone.