Relationship between electron field-aligned anisotropy and dawn-dusk magnetic field: nine years of Cluster observations in the Earth magnetotailстатья
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Дата последнего поиска статьи во внешних источниках: 16 ноября 2017 г.
Аннотация:We investigate the distribution and possible origins of thermal anisotropic electrons in the Earth's magnetotail, using nine years of Cluster observations. We mainly focus on relation between electron anisotropy and Bz, By magnetic field components (in GSM coordinates). The anisotropy of electron population is characterized by temperature ratio T∥/T⊥ and by the maximum of phase space density ratio F∥/F⊥(∥ and ⊥ are relative to the background magnetic field). The population identified by large F∥/F⊥ is organized as short-time (dozens of seconds) bursts with enhanced F∥ and can be observed even in the plasma sheet with small T∥/T⊥. The thermal anisotropy T∥/T⊥ is larger for times intervals characterized by stronger Bz and By: the strong By corresponds to the T∥/T⊥ peak around the magnetotail neutral plane Bx=0, whereas the strong Bz corresponds to larger T∥/T⊥ with a flat profile across the magnetotail. There is a dawn-dusk asymmetry: large T∥/T⊥ correspond mostly to strong Bz at the dusk flank and to strong By at the dawn flank. Using these differences of the electron anisotropy dependence on By and Bz, we discuss two possible mechanisms responsible for the anisotropy formation.