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 (approximate to 0.1MeV) electrons, different from the normal chorus. For high-energy (0.5MeV) 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.