Observations of relativistic electron microbursts in association with VLF chorus

The Solar, Anomalous and Magnetospheric Particle Explorer (SAMPEX) satellite frequently observes relativistic (>1 MeV) electron precipitation in the radiation belts at L shells of 4-6 with bursty temporal structure lasting <1 s. This phenomenon can occur at all local times but is most often seen between 0200 and 1000 magnetic local time. VLF chorus is also observed to occur preferentially at these same local times. Using electron observations from the SAMPEX satellite Heavy Ion Large Telescope and data from the Polar satellite plasma wave instrument, we show correlation between observations of relativistic electron microbursts and VLF chorus with frequencies <2 kHz. In addition, the duration of the individual rising frequency chorus elements is comparable to the duration of the relativistic electron microbursts. It has been speculated that relativistic electron microbursts are caused by wave-particle interactions, which strongly scatter electrons into the loss cone for a short period. Lower-energy electron microbursts in the range from tens to hundreds of keV have long been associated with chorus waves, since these lower-energy electrons can resonate at the equator with whistler-mode waves at chorus frequencies. Electrons of MeV energies do not satisfy the first-order cyclotron resonance condition with chorus wave frequencies at the equator. However, MeV electrons may interact with chorus through higher-order resonances or off-equatorial interactions.