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Another envelope soliton event below the H+ gyrofrequency and localized density depletion has been discoveredin the low auroral region (～1760 kin) by the Freja satellite. This envelope soliton has a characteristic frequencyat ～190 Hz, which is also close to the resonance frequency of hydrogen ion-oxygen ion hybrid wave. This event iscorrelated in time with the observations of the sharp increase of the ratio of oxygen ion density to hydrogen andwith the electron energization along the magnetic field. A theoretical model on the ion-ion hybrid wave excitedby an energetic electron beam has also been presented. It is found that the ion-ion hybrid wave is mainly excitedby the Cherenkov instability in the auroral region.