Relativistic Electron Microbursts as High‐Energy Tail of Pulsating Aurora Electrons

Abstract

In this study, by simulating the wave-particle interactions, we show that subrelativistic/ relativistic electron microbursts form the high-energy tail of pulsating aurora (PsA). Whistler-mode chorus waves that propagate along the magnetic field lines at high latitudes cause precipitation bursts of electrons with a wide energy range from a few kiloelectron volts (PsA) to several megaelectron volts (relativistic microbursts). The rising tone elements of chorus waves cause individual microbursts of subrelativistic/relativistic electrons and the internal modulation of PsA with a frequency of a few hertz. The chorus bursts for a few seconds cause the microburst trains of subrelativistic/relativistic electrons and the main pulsations of PsA. Our simulation studies demonstrate that both PsA and relativistic electron microbursts originate simultaneously from pitch angle scattering by chorus wave-particle interactions along the field line. Plain Language Summary Pulsating aurora electron and relativistic electron microbursts are precipitation bursts of electrons from the magnetosphere to the thermosphere and the mesosphere with energies ranging from a few kiloelectron volts to tens of kiloelectron volts and subrelativistic/relativistic, respectively. Our computer simulation shows that pulsating aurora electron (low energy) and relativistic electron microbursts (relativistic energy) are the same product of chorus wave-particle interactions, and relativistic electron microbursts are high-energy tail of pulsating aurora electrons. The relativistic electron microbursts contribute to significant loss of the outer belt electrons, and our results suggest that the pulsating aurora activity can be often used as a proxy of the radiation belt flux variations.

Multi‐Event Analysis of Plasma and Field Variations in Source of Stable Auroral Red (SAR) Arcs in Inner Magnetosphere During Non‐Storm‐Time Substorms

“…Figure 13b and 13c show that LBC waves at a frequency of ∼1 kHz coincided with the electron-flux enhancement. Because LBC waves are known to scatter electrons with energies of kiloelectronvolts to tens of kiloelectronvolts and cause diffuse aurora (e.g., Miyoshi et al, 2015Miyoshi et al, , 2020Thorne et al, 2010), they may have caused the observed increase of electron flux at energies of 10-20 keV with pitch angles near the loss cone and intensified the 557.7-nm emission at the equator edge of the diffuse aurora.…”

A Strong Correlation Between Relativistic Electron Microbursts and Patchy Aurora

“…The link between pulsating aurora and relativistic microbursts is observationally elusive, but has been theoretically proposed. Recent test-particle simulations by Chen et al (2020) and Miyoshi et al (2020) show that whistler-mode chorus rising tone elements can scatter keV-MeV microburst electrons. Miyoshi et al (2020) went on to hypothesize that relativistic microbursts are the high-energy tail of pulsating aurora.…”

Simultaneous Pulsating Aurora and Microburst Observations With Ground‐Based Fast Auroral Imagers and CubeSat FIREBIRD‐II

“…Their theory showed that relativistic electron (>500 keV) precipitation should have a positive energy dispersion (higher-energy electrons are precipitated later) following a negative energy dispersion of the low energy component (lower energy electrons are precipitated later). Miyoshi et al (2020) proposed a hypothesis stating that relativistic electron microbursts have the same origin as the pulsating aurora. That is, chorus waves cause electron scattering in a wide energy range from a few keV to more than several MeV if the chorus waves can propagate to higher latitudes.…”