Ionospheric Oxygen Outflows Directly Injected Into the Inner Magnetosphere: Van Allen Probes Statistics

Abstract

AbstractIonospheric oxygen outflows (IOOs) are frequently observed in Earth's inner magnetosphere. As a potential fast mass source of the inner magnetosphere, they have been extensively studied for decades. In this study, we identified 271 IOO events from 6‐year Van Allen Probes (VAPs) data and conducted a statistical study to reveal when, where, and how they occur. All the events are observed in the nightside magnetosphere, with the occurrence rate peaking at the L‐shells corresponding to the auroral oval. The spatial scale of IOOs in the equatorial plane is estimated from the two‐spacecraft configuration of the VAP mission. The results show that, in statistics, IOOs are 3.9‐hr wide in magnetic local time and 1.0‐Earth radius wide in L‐shell. Further investigation shows that IOOs would shift to lower L‐shells and occupy a larger L‐shell extent as the AE index increases. Analysis of the environment conditions reveals that IOOs are statistically associated with AE‐index enhancements, ultra‐low‐frequency (ULF) waves, and magnetic field dipolarization, but not with any systematic variations in the SYM‐H index and the solar wind parameters. From this observation, we suggest that geomagnetic substorms and substorm‐associated processes (e.g., ULF waves) are potential triggers of inner‐magnetosphere IOOs.