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Abstract To study the average contributions of the cusp outflow through the lobes and of the nightside auroral outflow to the O⁺in the plasma sheet (PS), we performed a statistical study of tailward streaming O⁺in the lobes, plasma sheet boundary layer|the plasma sheet boundary layer (PSBL) and the PS, using MMS/Hot Plasma Composition Analyzer (HPCA) data from 2017 to 2020. Similar spatial patterns illustrate the entry of cusp‐origin O⁺from the lobes to the PS through the PSBL. There is an Y_GSM‐dependent energy pattern for the lobe O⁺, with low‐energy O⁺streaming closer to the tail center and high energy (1–3 keV) O⁺streaming near the flanks. Low energy (1–100 eV) O⁺from the nightside auroral oval is identified in the near‐Earth PSBL/PS with high‐density (>0.02 cm⁻³), and energetic (>3 keV) streaming O⁺with similar density (∼0.013 cm⁻³) is observed further out on the duskside of the PSBL/PS. The rest of the nightside auroral O⁺in the PSBL is mixed with O⁺coming in from the lobe, making it difficult to distinguish the source. We estimated the contributions of the different sources of H⁺and O⁺ions through the PS between 7 and 17 R_E, using estimates from this work and data extracted from previous studies. We conclude that, during quiet times, the majority of the near‐Earth PS H⁺are from the cusps, the polar wind and Earthward convection from the distant tail. Similarly, while the O⁺in the same region has a mixed source, cusp origin outflow provides the highest contribution. 

Abstract Previous simulations have suggested that O⁺outflow plays a role in driving the sawtooth oscillations. This study investigates the role of O⁺by identifying the differences in ionospheric outflow between sawtooth and non‐sawtooth storms using 11 years of FAST/Time of flight Energy Angle Mass Spectrograph (TEAMS) ion composition data from 1996 through 2007 during storms driven by coronal mass ejections. We find that the storm's initial phase shows larger O⁺outflow during non‐sawtooth storms, and the main and recovery phases revealed differences in the location of ionospheric outflow. On the pre‐midnight sector, a larger O⁺outflow was observed during the main phase of sawtooth storms, while non‐sawtooth storms exhibited stronger O⁺outflow during the recovery phase. On the dayside, the peak outflow shifts significantly toward dawn during sawtooth storms. This strong dawnside sector outflow during sawtooth storms warrants consideration.