[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P09] Pitch-angle distribution analysis of energetic electrons using Arase (HEP) satellite

*Pankaj Kumar Soni¹、Yoshizumi Miyoshi¹、Tomoaki Hori¹、Takefumi Mitani²、Takeshi Takashima²、Iku Shinohara²、Ayako Matsuoka³ (1.ISEE Nagoya University、2.ISAS/JAXA、3.Kyoto University)

キーワード：Eartch's Magnetosphere, Pitch-angle Distribution

We have investigated the pitch-angle distribution of energetic electrons (~100 keV – ~ 1MeV) from March 2017- December 2023 in the outer radiation belt during CME- and CIR-driven geomagnetic storms using ERG (HEP, and MGF) measurements. We selected the geomagnetic storms with SYM-H less than -40 nT. During the storm intervals, pitch angle resolved electron flux data is obtained, and divided in the four phases of storms. The observed pitch-angle data is fitted in terms of Legendre polynomials accurate up to sixth order, and Legendre coefficients c2, and c4, along with the ratio R = |c2/c4| are used to categorize the different pitch-angle distribution types. We classified the pitch-angle distributions into three types: pancake, butterfly, and flattop. To resolve the pitch-angle distributions for different sectors, the derived coefficients are binned in 5 L-values, and 12 MLT bins for 8 energy channels. With this analysis, we found that the several hundreds of keV electrons have a dependence on the local time, and on the different phases of the geomagnetic storm. The pitch-angle distribution is observed butterfly type in the night side at higher L-values, while in the day side is mostly dominated by the pancake distribution. In addition, the pancake distribution recovers after the main phase of storm. Currently we are analysing the dependency of these different type of pitch-angle distribution on the source (CME/CIR) of geomagnetic storms.