[P-EM11] Dynamics of Magnetosphere and Ionosphere

[PEM11-14] Analysis on anisotropy variations for pitch angle distributions of electrons with various parameters at dipolarization sites in the inner plasma sheet

*Kaiti Wang¹、Zhuo-Ren Lang²、Ching-Huei Lin³、Tohru Hada⁴、Toshi Nishimura⁵ (1.Tamkang Univ.、2.National Cheng Kung Univ.、3.Chien-Hsin Univ. of Sci. & Tech.、4.Kyushu Univ.、5.Boston Univ.)

キーワード：dipolarization, anisotropy of pitch angle distributions of electrons , observations of THEMIS mission

During geomagnetic activities, dipolarization of geomagnetic fields can been found to occur at tailside. In this study, we investigate variations in anisotropies of pitch angle distributions for electrons at 63 observed dipolarization sites around distance of 10 R_E (Earth radii) near the magnetic equator in the inner plasma sheet when auroral electrojet AL index decreases. Observational data from 2008 to 2011 for electrons below ~26 keV from the instrument ESA (ElectroStatic Analyzer) onboard of THEMIS mission are adopted. Followed from our previous presentation in which the dependence of these variations on field line lengths (FLL) was focused on [Wang et al., 2018], we present new analysis results concentrating on the dependence of the changes as well as the rates of changes in FLL, magnetic field strengths, and dipolarization angles, during a dipolarizaion period. Comparisons between the anisotropy variations in pitch angle distributions of electrons and the associated bounce time of electrons, event dipolarization time, and measured environmental electric fields will also be presented and discussed.

References
Wang, K., Z. R. Lang, C. H. Lin, T. Hada, A. B. C. Chen, Y. Nishimura (2018). On the field line length dependence of variations in anisotropies for pitch angle distributions of keV electrons at dipolarization sites in the tailside. PEM16-25, JpGU Meeting 2018, Chiba, Japan.