Relativistic electron microbursts

Abstract

We report the first satellite observations of relativistic (>1 MeV) electron precipitation in microbursts with measured durations of less than 1 s. Microbursts of lower-energy electrons (10-100 keV) have been found to occur preferentially in the early daylight hours and to be closely associated with VLF chorus emissions. In contrast, the relativistic electron microbursts occurred more frequently near 2230 LT than 1030 LT, and no association was found with ELF/VLF chorus, consistent with the fact that resonant interactions with --• 1-MeV electrons require significantly lower frequencies. The available data on these relativistic microbursts thus appear to indicate that many of the bursts may be due to wave-particle interaction not with whistler mode chorus but possibly with other waveforms. The locations of many of the relativistic microbursts are concentrated at the outer edge of the trapped radiation belt, where the gyroradii of the electrons are comparable to the curvature of the magnetic field lines and stable trapping may therefore not occur. The preferred location of the microbursts, which may be primarily spatial in character, implies the possible importance of irregularities in the magnetic field lines near the trapping boundary as the responsible mechanism. 13,829 13,830 IMHOF ET AL.' RELATIVISTIC ELECTRON MICROBURSTS

Anisotropic pitch angle distribution of ~100 keV microburst electrons in the loss cone: measurements from STSAT-1

“…On the other hand, Imhof et al (1992) and Nakamura et al (2000) reported observations of impulsive electron precipitation with energies >1 MeV on polar orbiting spacecraft and called them relativistic microbursts (Blake et al, 1996;O'Brien et al, 2004). It is known that relativistic microbursts are associated with large amplitude whistler mode waves (Johnston and Anderson, 2010;Kersten et al, 2011).…”

The Balloon Array for RBSP Relativistic Electron Losses (BARREL)

“…Microbursts were later shown to extend to relativistic energies (Imhof et al 1992), and studied extensively with data from the SAMPEX satellite (e.g., Blake et al 1996;Nakamura et al 2000;). The top panel of Fig.…”

Short-duration Electron Precipitation Studied by Test Particle Simulation

“…The timescales of chorus waves are similar to those of electron microbursts, and the coincident occurrence of microbursts and VLF chorus waves supports the idea that microbursts are produced by resonant interactions between electrons and cyclotron waves (Rosenberg et al 1981). Imhof et al (1992) and Nakamura et al (2000) reported observations of impulsive electron precipitations with energies exceeding 1 MeV by spacecraft; these precipitations were named relativistic microbursts. However, relativistic microbursts have not been observed by balloon-borne experiments, and at this time it is unknown whether these microburst phenomena are related or originate from the same source.…”