Outflowing ion beams forming four successive inverted-V structures in the energy-time spectrograms of H+, He+, and O+ were observed at an altitude of 3.4 RE by Cluster satellites travelling above the auroral acceleration region (AAR) in the southern hemisphere on February 14, 2001. Energization by negative U-shaped potential structures in the AAR is believed to be responsible for the formation of these outflowing ion inverted-V structures. Thus, utilizing the different motion properties of the three ion species, the altitude of the upper boundary of the AAR is estimated to be ~11100 km. Moreover, based on multi-satellite observations, each of these U-shaped potential structures involved in this event crosses the latitudinal direction at ~0.4°–1° invariantlatitude (ILAT), moving poleward at an average speed of ~0.2° ILAT per minute, before disappearing at ~71.5° ILAT. Outflowing ion beams forming four successive inverted-V structures in the energy-time spectrograms of H +, He +, and O + were observed at an altitude of 3.4 RE by Cluster satellites traveling above the auroral acceleration region (AAR) in the southern hemisphere on February 14 , 2001. Energization by negative U-shaped potential structures in the AAR is believed to be responsible for the formation of these outflowing ion inverted-V structures. Thus, utilizing the different motion properties of the three ion species, the altitude of the upper boundary of the AAR is estimated to be ~ 11100 km. Further, based on multi-satellite observations, each of these U-shaped potential structures involved in this event crosses the latitudinal direction at ~ 0.4 ° -1 ° invariantlatitude (ILAT), moving poleward at an average speed of ~ 0.2 ° ILAT per minute, before disappearing at ~ 71.5 ° ILAT.