17:15 〜 18:45
[PEM13-P02] Statistical Survey of Energetic Electron Precipitation Observed by the Arase Satellite
キーワード：電子降り込み、波動粒子間相互作用、あらせ
Energetic electron precipitation from the magnetosphere into the upper atmosphere driven by the wave-particle interactions has received a lot of attention (e.g. microbursts, relativistic electron precipitation (REP), pulsating aurora). Pulsating aurora (PsA) is thought to be occurring when tens of keV electrons trapped into the inner magnetosphere are scattered into the loss cone by whistler-mode chorus waves generated near the magnetic equator and thereby fall into the upper atmosphere. Kasahara et al. (2018) has demonstrated that the resonant scattering by chorus waves causes the auroral pulsation, by showing a correlation between switch on / off from whistler wave activities and the modulation in the loss cone electron flux. The detailed correlation study was enabled by the high angular resolution, sufficient to resolve small loss cones, of the Medium-Energy (10-90keV) Particle experiments - electron analyzer (MEP-e) onboard the Arase satellite.
Based on the results by Kasahara et al. (2018), we try to statistically examine the contribution of wave-particle interaction to energetic electron fluxes inside the loss cone using MEP-e. In the case of the Earth's magnetosphere, the loss cone angle is about a few degrees. We therefore analyzed the distribution of electron fluxes whose pitch angle is <2 degrees and >178 degrees from March 2017 to March 2022 to clarify the observation occurrence frequency and spatial distribution of precipitating electrons.
The result shows that precipitating electrons are observed around L=6 from the nightside to the dawnside. This result is consistent with the region where whistler-mode chorus waves are generated [e.g., Teng et al. (2019)]. Therefore, the electron precipitation is considered to be occurring as the result of the wave-particle interaction with the whistler waves.
The result also displays that as the energy of the precipitating electrons increases, the high occurrence probability region of electron precipitation moves later magnetic local time (MLT). The energy-MLT dependance is shown by the ground observation by the EISCAT radars (Hosokawa and Ogawa., 2012): the central altitude of the PsA ionization decreases in the later MLT sector. We regard this MLT dependence on the precipitating electron energy also as the effect of the wave-particle interaction and could be explained by the increase in the parallel resonance energy of the first-order cyclotron resonant scattering in the later MLT. Here we discuss the validity of the interpretation of the result mentioned above.
Based on the results by Kasahara et al. (2018), we try to statistically examine the contribution of wave-particle interaction to energetic electron fluxes inside the loss cone using MEP-e. In the case of the Earth's magnetosphere, the loss cone angle is about a few degrees. We therefore analyzed the distribution of electron fluxes whose pitch angle is <2 degrees and >178 degrees from March 2017 to March 2022 to clarify the observation occurrence frequency and spatial distribution of precipitating electrons.
The result shows that precipitating electrons are observed around L=6 from the nightside to the dawnside. This result is consistent with the region where whistler-mode chorus waves are generated [e.g., Teng et al. (2019)]. Therefore, the electron precipitation is considered to be occurring as the result of the wave-particle interaction with the whistler waves.
The result also displays that as the energy of the precipitating electrons increases, the high occurrence probability region of electron precipitation moves later magnetic local time (MLT). The energy-MLT dependance is shown by the ground observation by the EISCAT radars (Hosokawa and Ogawa., 2012): the central altitude of the PsA ionization decreases in the later MLT sector. We regard this MLT dependence on the precipitating electron energy also as the effect of the wave-particle interaction and could be explained by the increase in the parallel resonance energy of the first-order cyclotron resonant scattering in the later MLT. Here we discuss the validity of the interpretation of the result mentioned above.