Characteristics of Field‐Aligned Low‐Energy Oxygen (FALEO) Events Based on Arase LEP‐i Observations

Abstract This study investigates field‐aligned low‐energy oxygen (FALEO) ions observed by the Arase satellite during 2020–2023. Using 4 years of data from the low‐energy particle experiment ion mass analyzer and magnetic field investigation instruments, we identified 90 energy‐dispersed FALEO events and our analysis reveals several key findings: (a) FALEO ions exhibit field‐aligned motion, appearing parallel to the magnetic field below the equator and anti‐parallel above it (b) the stop energy of nightside FALEO ions increases with L ‐value but decreases at low L ‐value during the high K p values, (c) unidirectional FALEO events occur primarily between 18 magnetic local time (MLT) and 08 MLT, peaking near 00 MLT, (d) bidirectional events are found between 22 and 10 MLT, with a broad maximum around 06 MLT, (e) for the first time, using Arase bidirectional FALEO events are observed on the dawnside magnetosphere within 06–10 MLT, and (f) most of the dawnside FALEO events are associated with geomagnetic storms, indicating a strong link to enhanced geomagnetic activity. These findings suggest the existence of a previously unrecognized dawnside source of FALEO ions in addition to the well‐established nightside source. The presence of such events on the dawnside may impact dayside reconnection processes and affect the global magnetospheric convection.