Distribution of Singly-Charged Oxygen Observed in a High-Density Region Flowing Tailward in the Plasma Sheet by GEOTAIL at X_GSE ∼ -60Re

Abstract

We report an observation of the singly-charged oxygen ions (O⁺) in the plasma sheet at X_GSE∼ -60Re. Observed structures in the intensity and angular distribution of O⁺ ions correlated with a localized high-density region and large-scale changes in the proton flow direction. The average energy of O⁺ was much higher than that of the main component (H⁺). The tailward flowing high-density region containing O⁺ ions caused the drastic flow variations in the north-south meridional plane in the plasma sheet. The anisotropic O⁺ distribution probably by finite gyroradius effect was observed just before the density enhancement, while the O⁺ flow direction was the same as that of the proton bulk flow in the high-density region.