Characteristics of Electron Microburst Precipitation Based on High‐Resolution ELFIN Measurements

• Published in: Journal of geophysical research. Space physics 2022-05, Vol.127 (5), p.n/a
• Main Authors: Zhang, Xiao‐Jia, Angelopoulos, Vassilis, Mourenas, Didier, Artemyev, Anton, Tsai, Ethan, Wilkins, Colin
• Format: Article
• Language: English
• Subjects: Amplitudes; Atmospheric models; Bursts; Chorus waves; Cubesat; ducted chorus waves; Earth orbits; Earth's radiation belts; Electron flux; Electron flux measurements; Electron microbursts; electron precipitation; Energy spectra; energy spectrum; Equator; Geomagnetic activity; geomagnetic substorms; Latitude; Low earth orbits; microburst; Microbursts; Microbursts (meteorology); Modelling; Precipitation; Radial distribution; Radiation; Radiation belts; Resonant interactions; Scattering; Spacecraft; Statistical models; Wave packets; Wave propagation
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2022JA030509

We present statistical characteristics of electron microburst precipitation using high time‐resolution measurements from the low‐altitude Electron Losses and Fields InvestigatioN (ELFIN) CubeSats. The radial distribution of the equatorial projection of microbursts as a function of geomagnetic activity suggests that they are produced by resonant interaction with quasi‐parallel lower‐band chorus waves. ELFIN electron flux measurements provide the first statistical models of microburst energy spectra from 50 keV to 2 MeV. Microbursts with energies up to 150 keV have a relatively flat pitch‐angle spectrum. Estimates of scattering rates required to produce the observed flat spectra suggest that such precipitation signatures are due to near‐equatorial electron scattering by chorus wave packets with peak amplitudes of 0.4–0.9 nT, well above the threshold for nonlinear resonant interaction. More rare microbursts, exceeding 500 keV, are observed preferentially near dawn during disturbed periods. We interpret them as evidence of scattering by intense ducted chorus waves propagating from the equator up to middle latitudes with little attenuation. Plain Language Summary Electron microbursts are extremely intense and transient bursts of precipitation from the Earth's radiation belts into the atmosphere, with typical sizes of 20–30 km at low Earth orbit and 100–200 km near the equator. The integral contribution of such precipitation bursts can be substantial for radiation belt dynamics. Their bursty nature, however, questions the applicability of standard electron diffusive models. Different spacecraft have detected microbursts in very different energy ranges, from tens of keV to MeVs, and most of these observations suggest that microbursts are generated by electron resonant scattering by very intense packets of whistler‐mode chorus waves. In this study, we provide the first statistical model of microburst energy spectra from 50 keV to 2 MeV. We have also shown that the wave amplitude required to produce the observed microbursts is so large that classical diffusive models of electron scattering by waves would not work. This implies that microbursts are likely produced by electron nonlinear resonant interactions with intense chorus waves that probably propagate ducted inside field‐aligned density enhancements up to the latitude of resonance with electrons. Key Points Statistical study of microburst energy spectrum from 50 keV to 2 MeV shows that the mean energy increases