[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P11] Observed marginal condition of electron temperature anisotropy instability in the inner magnetosphere

*Iku Shinohara¹, Jingxuan Yang, Yoichi Kazama², Shiang-Yu Wang², Chae-Woo Jun⁶, Satoshi Kasahara³, Shoichiro Yokota⁴, Kunihiro Keika³, Tomoaki Hori⁶, Kazushi Asamura¹, Takefumi Mitani¹, Ayako Matsuoka⁵ (1.Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science, 2.ASIAA, 3.University of Tokyo, 4.Osaka University, 5.Kyoto University, 6.Nagoya University / Institute of Space-Earth Einvironmental Research)

Keywords:whistler wave, electron temperature anisotropy, inner magnetosphere

The Whistler chorus waves play a crucial role in the acceleration and loss of high-energy electrons in the Earth's inner magnetosphere. These waves are excited by the possible free energy of electron temperature anisotropy, which is provided by injections from the magnetotail. However, the distribution of electron temperature anisotropy is not well understood due to a lack of plasma observations in the inner magnetospheric region.
To investigate this, we studied electron temperature anisotropy using data from the Arase satellite, specifically electron data (LEP-e and MEP-e) observed from March 2017 to October 2019. Our findings indicate that the marginal condition of the whistler anisotropy instability can be identified in the data obtained near the magnetic equator. The data points located near the marginal condition are within a limited region of L_m=5~6, MLT=23~6, and MLAT=-10~+10, which is consistent with the higher occurrence region of the whistler chorus wave in the inner magnetosphere.
Significant data points were observed during the geomagnetically active phase at AE>300, and the duration when the marginal condition is satisfied is within a few minutes. We will further discuss the time and spatial evolution of temperature anisotropy based on the Arase observation in this presentation.