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 0.1–0.8fce_eq (with the equatorial electron gyrofrequency fce_eq). We here report an event of intense low‐frequency chorus with nearly half of wave power distributed below 0.1fce_eq 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. Key Points Intense low‐frequency chorus observed by Van Allen Probes Low‐frequency chorus exhibited hiss‐like signatures most of the time Low‐frequency and normal chorus waves have different electron diffusion rates