Japan Geoscience Union Meeting 2021

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[E] Oral

P (Space and Planetary Sciences ) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM09] Dynamics of Magnetosphere and Ionosphere

Sun. Jun 6, 2021 9:00 AM - 10:30 AM Ch.05 (Zoom Room 05)

convener:Akiko Fujimoto(Kyushu Institute of Technology), Mitsunori Ozaki(Faculty of Electrical and Computer Engineering, Institute of Science and Engineering, Kanazawa University), Yuka Sato(Nippon Institute of Technology), Aoi Nakamizo(Applied Electromagnetic Research Institute, National Institute of Information and Communications Technology), Chairperson:Hiroshi Hasegawa(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), Masaki N Nishino(Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science)

9:35 AM - 9:50 AM

[PEM09-04] Energy dependence of field-aligned anisotropy of electrons during dipolarization at Earth's tailside

*Kaiti Wang1, Ching-Huei Lin2, Zhuo-Ren Lang3, Tohru Hada4, Toshi Nishimura5 (1.Tamkang Univ., 2.Chien-Hsin Univ. of Sci. & Tech., 3.National Cheng Kung Univ., 4.Kyushu Univ., 5.Boston Univ.)

Keywords:dipolarizations in the inner plasmasheet, field-aligned anisotropy of electrons, energy-dependence, AL index, electric fields, observations of THEMIS mission

A specific pattern on energy-dependence of variations in field-aligned anisotropy (η) of electrons was found from hundreds of eV to thousands of eV during dipolarization time around 10 Earth radii near magnetic equator in the inner plasmasheet at tailside based on measurements of the instrument ESA (ElectroStatic Analyzer) onboard of THEMIS Mission. More exactly, in the beginning of dipolarization, η peaks at a lower energy and it shifts to a higher energy but with a smaller value when the dipolarization angle reaches maximum [Wang et al., 2019]. In this study, by further analyzing the field-aligned anisotropies of electrons in both northward and southward directions at 62 dipolarization sites from the year of 2008 to 2011, we find that electrons observed at about two-thirds of these sites exhibit such a pattern and the energy range is largely associated with the ratio of bounce time to the dipolarization time. Furthermore, we find that this pattern hardly exists when the minimum AL index is less than -190nT or the maximum of y-component of electric field (Ey) measured by the onboard instrument EFI (Electric Field Instrument) is higher than 20mV/m during the dipolarization time analyzed. Hence, mechanisms affecting electron motions associated with the values of AL index and Ey as well as their influences on this energy-dependence will be assessed and discussed.

*References

Wang, K., Z. R. Lang, C. H. Lin, T. Hada, T. Nishimura (2019), Analysis on anisotropy variations for pitch angle distributions of electrons with various parameters at dipolarization sites in the inner plasma sheet, Paper No. PEM11-14, JpGU Meeting 2019, Chiba, Japan.