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 0.1-0.8f_ce-eq (with the equatorial electron gyrofrequency f_ce-eq). We here report an event of intense low-frequency chorus with nearly half of wave power distributed below 0.1f_ce-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.