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

Abstract

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.

Quantifying the Size and Duration of a Microburst‐Producing Chorus Region on 5 December 2017

“…The latitudinal propagating chorus waves cause wide energy electron precipitations from keV energy (pulsating aurora) and MeV energy (relativistic electron microbursts) because the resonance energy depends on the magnetic latitudes. This model is consistent with recent studies that use conjugate observations between ground-based observations and SAMPEX and FIREBIRD (Kawamura et al, 2021;Shumko et al, 2021;Zhang et al, 2022).…”

On the Nature of Intense Sub‐Relativistic Electron Precipitation

“…The energy range of microburst precipitation is quite wide (e.g., Zhang, Angelopoulos, et al., 2022): there are both relativistic microbursts (Blum, Li, & Denton, 2015; O’Brien et al., 2004), microbursts of few hundreds of keV (Capannolo et al., 2019; Shumko, Sample, et al., 2018), and even of tens of keV (Blake & O’Brien, 2016). Moreover, recent investigations show strong correlations between relativistic microbursts and tens of keV electron precipitation responsible for diffuse aurora (Y. Miyoshi et al., 2020; K. Miyoshi Y. et al., 2021; Shumko et al., 2021).…”

“…(2015); Grach and Demekhov (2020)). The most intense whistler‐mode and EMIC waves interact with electrons nonlinearly (see reviews by Shklyar & Matsumoto, 2009; Albert et al., 2013; Artemyev, Neishtadt, Vainchtein, et al., 2018, and references therein) providing very intense and bursty precipitation events, called microbursts (Blum, Li, & Denton, 2015; Breneman et al., 2017; Capannolo et al., 2019; O’Brien et al., 2004; Shumko, Turner, et al., 2018; Zhang, Angelopoulos, et al., 2022). There exist many theoretical models of microbursts generated by whistler‐mode waves (e.g., L. Chen et al., 2020; L. Chen et al., 2021) and EMIC waves (e.g., Kubota & Omura, 2017).…”

On the Incorporation of Nonlinear Resonant Wave‐Particle Interactions Into Radiation Belt Models

“…In the opposite but more frequent case of unducted wave propagation, the waves would rapidly become more oblique and, in general, would be heavily damped before reaching the latitude of resonance with 1 MeV electrons (Chen et al., 2021). Consequently, the time intervals with intense, ducted chorus waves should be characterized by a faster increase of 1‐MeV electron flux and by stronger precipitations of 1‐MeV electrons (Chen et al., 2022; Miyoshi et al., 2020; Zhang, Angelopoulos, et al., 2022) than in calculations assuming a purely quasi‐linear electron diffusion (Mourenas, Artemyev, Agapitov, & Krasnoselskikh, 2014; Mourenas, Artemyev, Agapitov, Krasnoselskikh, & Li, 2014), but it may not be the case during the more frequent periods with unducted wave propagation.…”