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 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.
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論文編號: PEM09-04, Japan Geoscience Union Meeting 2021
