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.

Energy‐Resolved Detection of Precipitating Electrons of 30–100 keV by a Sounding Rocket Associated With Dayside Chorus Waves

“…Another possible case is that resonance occurred only at the high magnetic latitude, where the magnetic field is stronger than the magnetic equator. Suppose the chorus waves of < were generated at the equator in the slightly higher L‐shell region (e.g., the magnetic field intensity ∼ 70 nT) and obliquely propagated to the magnetic field line of the rocket trajectory, up to the latitude of 25° (the magnetic field intensity ∼ 180 nT), the 30 keV electrons are no longer in resonance (e.g., Miyoshi, Saito, et al., 2015; Miyoshi et al., 2020). This explains the observed energy spectrum, where the flux of ∼30 keV is absent compared to that of ∼50 keV.…”

“…Precipitating electrons from the magnetosphere have been measured by balloons, sounding rockets, and low‐altitude satellites to investigate auroral zone phenomenology (e.g., Fuller‐Rowell & Evans, 1987; Miyoshi et al., 2010; Miyoshi, Oyama, et al., 2015; Winningham et al., 1975), radiation belt dynamics (e.g., Millan & Thorne, 2007; Miyoshi et al., 2008) and effects on the chemical composition of the upper atmosphere (e.g., Lam et al., 2010; Miyoshi, Saito, et al., 2015; Miyoshi et al., 2020; Thorne et al., 1977; Turunen et al., 2016). Hardy et al.…”

Rocket Observation of Sub‐Relativistic Electrons in the Quiet Dayside Auroral Ionosphere

“…A likely explanation for these electrons is the pitch angle scattering of electrons in the dayside magnetosphere due to wave‐particle interactions with whistler‐mode waves, which are suggested from the complementary ground and satellite observations during the RockSat‐XN observation (Figures 4 and 5). Whistler‐mode waves can interact with high‐energy electrons when they propagate to high latitude because the resonance energy increases with increasing the background magnetic field strength (Horne & Thorne, 2003; Miyoshi et al., 2010, 2020; Miyoshi, Oyama, et al., 2015). For example, the equatorial chorus wave amplitude distribution for AE ≤ 100 nT is highest in the dawn MLT sector (7–13 MLT) (Li et al., 2009) and these dayside chorus waves show little dependence of occurrence on geomagnetic activity (Spasojević & Inan, 2010; Tsurutani & Smith, 1977).…”

Data‐Driven Simulation of Rapid Flux Enhancement of Energetic Electrons With an Upper‐Band Whistler Burst

“…By using the above sequence of calculations, we can solve the equations of magnetic mirror motion coupled with the equation of motion in electromagnetic fluctuations of whistler mode waves propagating along the field line. The RBW model has been successfully applied to various wave‐particle interaction phenomena in radiation belts, pulsating auroras, and microbursts (Miyoshi et al., 2020; Miyoshi, Oyama, et al., 2015; Miyoshi, Saito, et al., 2015; Saito et al., 2012; 2016).…”