Auroral particle acceleration due to quasi-electrostatic potential drops along the magnetic field lines at altiudes of∿1R_e is one of the most important topics in auroral and magnetospheric physics. With existence of such potential drops, the precipitating electrons observed below the acceleration region have an peak in the energy spectrum, while above the region the ionospheric ions are accelerated upward as Upward Flowing Ions (UFI), and the electron ditribution functions have an energy-dependent loss cone. Previous observations have only qualitatively supported such a view. In this paper we present a quantitative result that the detailed distribution functions of electrons and ions observed from Akebono have revealed existence of the E_∥ acceleration both above and below the spacecraft altitude.
極域磁気圏における粒子降下および加速機構の研究
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