[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-P04] A study of the energy of pulsating auroral electrons using simultaneous conjugate observations by Arase satellite, EMCCD all-sky imager and EISCAT radar

*Yuri Ito¹, Keisuke Hosokawa¹, Yasunobu Ogawa², Yoshizumi Miyoshi³, Shin-ichiro Oyama³, Satoko Nakamura³, Yoshiya Kasahara⁴, Shoya Matsuda⁴, Iku Shinohara⁵ (1.The University of Electro-Communications, 2.National Institute of Polar Research, 3.Institute for Space-Earth Environmental Research, Nagoya University, 4.Kanazawa University, 5.Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science)

Keywords:Pulsating aurora

When the magnetosphere is disturbed, high-energy electrons stored in the Earth's magnetosphere precipitated into the Earth's atmosphere along the magnetic field lines and excite atmospheric particles through collisions. The excited particles emit optical emission when they return to lower energy level state. Auroras are classified into two broad categories based on their shape: discrete auroras, which have a distinct shape, and diffuse auroras, which have an indistinct shape. Most of the diffuse auroras are known to show a quasi-periodic luminosity modulation and are called pulsating auroras (PsA). Magnetospheric electrons, which are scattered through the wave-particle interaction with "chorus waves" and precipitated into the ionosphere are called “PsA electrons”. Recent studies demonstrated that sub-relativistic electrons of radiation belt origin simultaneously precipitate into the ionosphere during intervals of PsA. This means that the loss process of such highly energetic electrons in the magnetosphere can be visualized by observing the form/distribution of PsA and the energy of PsA electrons. For this purpose, it is important to understand the factors that control the morphology of PsA and the energy of PsA electrons, which have not been clarified in previous studies.
In this study, the geospace exploration satellite Arase, the EMCCD all-sky imager, and the European Incoherent SCATer (EISCAT) UHF radar were used in combination for simultaneous observations of PsA. By using this data set, we investigated the relationship between the morphology of PsA and the energy of PsA electrons. The energy of PsA electrons was estimated from the altitude distribution of electron density obtained from the EISCAT- UHF radar and GLOW model (Solomon et al., 2017), and it was found to be consistent with the resonance energy of the chorus wave calculated from the observation of chorus waves by the Arase satellite. In addition, the energy of PsA electrons tended to change in accordance with the transition of the morphology of PsA. Specifically, when the spatial structure of PsA was clear (i.e., the boundary of the patch structure is distinct), the energy of the corresponding PsA electron exceeded 20 keV. This fact suggests that both the morphology of PsA and the change in the energy of PsA electrons are controlled by the existence of "ducts," tube-like regions where the electron density is lower or higher than the surrounding area, and resultant propagation of chorus waves to higher latitudes. In addition, the past observation showing that PsA energy is higher in the morning side than near midnight suggested that ducts are often formed in the later morning side, where chorus waves are allowed to propagate to higher latitude. In presentation, we will introduce the observational results and discuss the factors controlling the morphology of PsA and energy of PsA electrons.